As always with suspects, a fair way to proceed is to estimate the effects of the suspect on the tier. Obviously this isn't a perfect science, but we should at least try to see what everyone else is thinking. I'll restrict myself to this thread because I think it is comprehensive but outside conversations, even off Smogon, can be competitively relevant too if anyone wants to bring them in.
The OP started off by claiming Scizor is the most influential Pokemon in the tier, being threatening with Choice Band and Swords Dance. After this description, Pearl began narrate some of Scizor's effects on the tier:
All in all, Scizor is a threat that often forces people to sacrifice multiple slots on their teams in order to have all of its sets properly covered. Still, in spite of this fact, it is also a Pokemon that single handily prevents a ton of threatening sweepers from getting out of hand, which is one of the primary reasons why it has managed to find itself a comfortable place in the metagame up until recently.
His point - Scizor has many sets that can beat many of its counters and checks so it means you have to use several Scizor checks/counters per team. Additionally, he notes Scizor "single handily" stops many Pokemon from being broken. These are two effects Pearl posits exist.
Vivalospride mainly responded to the first effect Pearl mentioned. Namely, he expands on Pearl's point by pointing to some common UU matchups that demonstrate Pearl is correct, Scizor needs many Pokemon to check it. Amoonguss, Cobalion, Alomomola, and Infernape and others can check some Scizor sets but completely fail vs other sets. This covers both defensive and offensive checks notably.
Scizor gets around it's checks really easily and covering all it's variations of SD sets is really hard. Amoonguss/Alo/Other just bulky blanket check type mons can help with the CB sets, taking U-turns n shit but just aren't enough for SD. A lot of people rely on guss like their sciz matchup is aight and then +2 bug bite murders them, or +2 bug z, etc. Quick Attack makes a lot of the more frail sciz checks like nape pretty useless if you let it set up, and other checks like heattom hate switching into knock. Coba checks a lot of variations of sciz but there's always the fight z/cb superpower to look out for. Tenta checks but is frail af physically, and Doub doesn't immediately threaten it too much while it also doesn't check knock sets. Scizor shreds through teams and works around it's checks to an extent that's incomparable to anything else in the tier for sure. But it also is really the only thing stopping a lot of things from being too much in the tier. Malt and sd rak for example both have their fair share of checks, but in terms of offensively pressuring these mons there's nothing that does it more consistently than sciz. A lot of teams that have like guss/glig as their fighting resists rely on sciz to keep something like sd rak from winning. Idk i'm literally just rambling b/c as I said I have no idea what I'm voting, sciz has it's fair amount of checks and counters and all that for sure and I don't think it's broken by any means, but it's very very dominant w/o a doubt.
So we still have two effects - Pearl's point that Scizor forces you to run many checks or counters which is supported by Vivalospride's post where he finds actual match ups of this and Pearl's other point that Scizor helps keep many threats in check. This second point is developed further by Hogg, who more formally and more strongly states that Scizor actually makes team building easier. He expands on the obvious idea that Scizor checks Terrakion and Altaria and goes on to say that the fact can check basically everything not resistant to Steel means it is easier to build teams.
Anyhow, I'll post my full thoughts later, but I do plan to vote no ban. I think Scizor has an overall positive impact on the meta despite how difficult it is to defensively check. Yes, if you're running a defensive team, you probably do need to run redundant checks to it (though the same is true for things like Latias and Mega Altaria), but it also provides so much offensive utility in one little slot that I think it overall makes teambuilding easier, not harder. Scizor's strong Bullet Punch is an amazing check not just to things like Terrak/Alt/Aero but to basically everything that doesn't resist it, and it single-handedly (clawedly?) allows teams to get away with not running hard defensive answers to every single threat. I think the overall effect is to make teams less reliant on matchup fishing and in turn to make the metagame more robust. I'll elaborate a bit more when I have time, but that's where I stand right now.
So we still have the two original Pearl points - Scizor means you have to run many Scizor checks + Scizor itself checks many things in the tier. Moutemoute comes in from another direction and supposes there is a third effect of Scizor on the tier - some Pokemon that would be otherwise usable in UU are invalidated because of Scizor.
Scizor invalidates on its own some Pokemon from the lower tier which means we may be able to see some new Pokemon if Scizor had to leave the tier (I think about Pokemon which are pretty weak to Scizor's priority : Bullet Punch ; like Gardevoir, Whimsicott or Espeon). On this other, some Pokemon in Underused will be better like Nihilego.
Moutemoute also reiterates much of what has already been said by Pearl, Hogg, and Vivalospride in his analysis of Scizor. So now we have three effects - the first two Pearl mentioned of needing many Scizor checks + Scizor helping check many things plus Moutemoute's contention that Scizor is keeping many otherwise viable Pokemon out of UU.
CBU adds to Pearls first point, that Scizor needs many checks, by saying that Scizor's niche checks actually are otherwise decent still in UU. He points to Pokemon like Rotom-H and Doublade as Pokemon that can check at least a few of Scizor's sets while still being useful in the metagame overall. CBU is trying to say that even if the first point is true and you need many Scizor counters, it doesn't necessarily lead to a bad metagame.
Furthermore, i would like to adress the point that scizor forces certain meta trends that make UU more stale. I honestly tho cannot look at any mon that rose in usage because of scizor(gligar, rotom-h, doublade, rh cobalion) and say that they are gimmicks. All have uses outside of walling/checkin scizor. A true example of a pokemon having a toxic influence on the meta because of its broken status is latias forcing the triple dark on scarf krook, which outside of revenging latias is a bad set.
Now, we are at Pearl's two points that have been added on to by various users plus a third point by Moutemoute that Scizor might be keeping some otherwise good Pokemon outside of UU. Silvioguacamole adds to Pearl's first point. He fully acknowledges that Scizor needs many checks and counters for every game but says this doesn't mean much because this is true of all S and many A rank Pokemon. He also reiterates CBU's point that Scizor checks and counters are just fine in the metagame.
While it is true that Scizor has tools to bust past some of it's answers, the same can be said of pretty much any offensive threat past C rank: ignoring A+/S ranks, which should be self-evident
At risk of repeating myself, this is not a trait that is unique to Scizor. A lot of the issues that arise from the need to have multiple checks are in the builder, and in the need to account for all potential sets in battle. While Sciz does have a obvious effect on teambuilding (imagine having to account for S rank threats when building a team, oh the horror!) it's go-to checks and counter provide a ton of utlilty outside of checking Scizor. Common countermeasures to various sets in Hippowdon, Cobalion, Empoleon, Gligar, Aggron, Steelix, Nidoqueen, Z Krook, Swampert, Blastoise, Mantine, Rotom Heat, Tentacruel, Moltres and Volcanion all provide hazard utility and are generally pretty splashable. Other measures like Doublade, Manectric, Amoongus, Crawdaunt, Lucario, Suicune, Zeraora Jellicent and Infernape provide much, much more than just checking Scizor and none of these mons would see huge drops in usage with just a Scizor ban. While it may be true that there is no 'one size fits all' check to Scizor, or many other pokemon, the difficulty of maneuvering around Scizor in the builder is often overstated due to the utility and splashability of it's checks and counters.
We then engaged in several posts on tiering policy which you can read if it interests you, but my goal is to see what we estimated Scizor's effect is, which is independent of tiering policy.
Adaam's post did not really try to estimate Scizor's effect, but he did describe some of its weaknesses which is good background information for us to use. The typing has drawbacks offensively. The below average BP moves except Superpower mean Scizor is only strong. And of course, the Fire weakness.
Steel is mediocre at best offensively, and Bug is even worse. It is not hard to find any one of a Fire/Water/Steel/Electric type to check Scizor offensively. The Quick Attack set can circumvent some of these frailer checks like Infernape, Mega Sharpedo, or Starmie, but this set must forego Roost since a 3rd coverage move is desperately needed so it runs the risk of killing itself. It also has awful coverage (no Bug Bite means walled by Slowbro, no Superpower means walled by every Steel-type), so it trades a better offensive matchup for a bad fat one.
Admittedly, Scizor has the ability to chip its checks with U-Turn, and this is exasperated if SR is up. However, U-Turn is not a risk-free move that players can click to gain easy momentum. Often the user has to pick between clicking Bullet Punch on something like Terrakion, or predict the switch and U-Turn. Picking wrong, especially in the latter case of U-Turning incorrectly, can be disastrous as you take a lot of damage from the incoming hit and are left at a health where you are no longer effective. Of course, there are situations in which U-Turn is 100% free (like at a -2 Latias), but such a situation should be rewarded if a player puts himself at that position. Scizor often finds itself in favorable positions, yes, but not so much that it needs to be banned.
Another point I want to make involves playing around an opponent's Scizor. SM UU is a tier with so many terrifying breakers and sweepers that, in my opinion, the best way to prep for them is to limit their switch-ins rather than seek to have sturdy defensive counterplay. Scizor is no different. Limiting its opportunities to generate free turns is key, and teching to do so is not herculean due to its 4x weakness to Fire and lack of immediate power. At the end of the day, 90 base power BP is nothing to write home about. HP Fire can be slapped on stuff like Latias and Celebi (or just a Z-move nuke), Babiri berry on Steel-weak Pokemon like Terrak/Toge, Foul Play Klefki, and Fire Blast Blissey.
Clefable comes from a different perspective, almost dismissing the premise that Pearl set up by saying Scizor is actually far stronger than implied. he agrees with Moutemoute's point that Scizor is stopping some otherwise usable Pokemon from entering UU. He goes further to call it disproportionately powerful. Again, Clefable is barely trying to estimate the effects of Scizor apart from his half sentence with Moutemoute's point. He's just contrasting with Adaam, who supposes that Scizor is just another normal threat, by describing Scizor as something that is exerting undue control over the tier.
But if you're one of the people who has known since the start of gen 7 how disproportionately powerful scizor is compared to the rest of UU, how it singlehandedly prevents mons such as slurpuff, cloyster, and forretress from seeing the light of day, how it shows up in 90% of games and provides the wincon, how it dissuades outsiders from UU from ever joining this static and boring tier, then you'll probably vote ban, and have no issues banning the rest of the obviously broken pokemon that pollute the UU S ranks.
Lastly, Jaajgko links to a previous post of his where he disagrees with Hogg, who in this thread said Scizor helps teambuilding. The fact that Scizor can easily beat some of its counters with the right set makes it hard too hard to play against and the fact that Scizor is so centralizing means its over prepared for and easily taken advantage of if its your only check to something.
Building good teams while needing two Scizor checks is possible and most players dealt with it but it puts a huge lock on the teambuilder as I often had to give up teambuilding ideas because I had to include a second Scizor check on top of having to check all the other threats. And I don't really feel like having Scizor in the tier eases teambuilding that much, it sure is a great revenge killer but in terms of defensive abilities it doesn't safely check a lot of mons since everybody preps for Scizor. If you want to check Altaria, you'll have to fear Fire Blast, if you want to check Latias, you'll have to fear Z-Thunder, Aero can run Fire Fang, +2 Celebi's Shattered Psyche destroys Scizor if it took a little bit of chip damage, Kyurem can run HP Fire, so most of the time you'll just be able to safely check bulky mons and set up on them. I am not denying the pressure Bullet Punch can put on the opponent but you can't go away with "I'll add a Scizor in my build a now I have a check to Altaria, Latias, Celebi and Aero". Actually if you want Scizor to check the mons I stated you'll usually have to run a non-optimal set like 244 HP + 92 SpD or Scarf / Assault Vest.
So globally, Scizor makes teambuiling in UU pretty challenging and removes a lot of options while itself not providing much defensive utility to ease up builds, and actually lets potentially broken mons stay in UU because it stops them from sweeping while on top of that being one of the scariest end game sweeper in the metagame with its SD sets one of the strongest wallbreaker with its Choice Band set. I think Scizor has a negative impact on the metagame and should be banned along with the other problematic mons it keeps in check.
So where have we gone? We still have the original Pearl point that Scizor needs many checks, but we qualified that saying the checks are not that hard to fit on, are otherwise good, and this isn't very special for an S rank. We also developed Pearl's point that Scizor checks many threats by saying it might make teambuilding easier. The flip side of this is Moutemoute's point that Scizor might be keeping otherwise good Pokemon out of UU. We think a la Adaam Scizor might just be another Pokemon with exploitable weaknesses or a la Clefable Scizor is something
Disclaimer: I know Pearl and others are not the only nor are the only persons who thought of these points as I refer to them. Names just makes following the debate easier. All I did was try and summarize.
