I'm going to make my standpoint on Shadow Tag very clear in this post, and I know for a fact that I am going to get a lot of backlash for what I am going to say. So before I make my post I'm going to say that I don't want to completely derail the thread. Please don't get hotheaded if you choose to respond to me, and I am giving express permission for anyone to flat out sling abuse at me through PM during the next few days - just don't derail the thread to do so. Anyway, here goes nothing.
I don't think that Shadow Tag itself should be banned. While I respect why it is on suspect, and I get the stigma surrounding it, I personally don't really understand why Shadow Tag should be considered noncompetitive while other trapping abilities get of scot-free (I will elaborate on this better than this during my post, so don't let this crappy first paragraph put you off). STag is being suspected on the basis that it prevents the opponent from switching out... but doesn't this also apply to Arena Trap and Magnet Pull?
While I'm not saying that we need to ban Magnet Pull any time soon, the point I was trying to make there was that it is not actually the trapping element of this game which I feel is problematic. At the end of the day, switching out is one mechanic and having an ability that prevents doing so is another. We are on a fourth generation of Magneton/Magnezone trapping steels and Dugtrio trapping anything grounded, and they neither have or ever will get the same treatment as I see today with Shadow Tag. Why? There is one reason:
The mechanic of switch prevention is only as noncompetitive/broken as its user.
As far as users of trapping abilities go in all stages of generation 6 OU, there have been six viable users (Mega Gengar, Gothitelle, Wobbuffet, Dugtrio, Magnezone and Magneton) and two which only see use on tri/quad trapper teams (Gothorita and Wynaut). In PU, we have Trapinch, and I won't bring up LC as it is out of the "hierarchy" of tiers. Of these nine Pokemon, one has been banned (Mega Gengar), and two are hated by the OU community (Gothitelle and Gothorita). What do these three have in common, and what makes the other six different? The difference is this: Mega Gengar, Gothitelle and Gothorita are all capable of doing more than just trap.
In my opinion, a trapper is only a problem if it is capable of either beating all archetypes without sacrificing effectiveness or if it can actively take advantage of what it traps without sacrificing effectiveness. Gengar's ability to both outpace and eliminate basically everything not blob-shaped in the tier made it broken/noncompetitive as a supporter, while Gothitelle and Gothorita's ability to cripple the opponent's answer to stall with TrickScarf while also potentially taking advantage of them with Calm Mind makes them noncompetitive. These are not healthy Pokemon for the metagame. However, these are the only things that give switch prevention this percieved noncompetitiveness. Beyond this, trappers need to either sacrifice effectiveness to take advantage of what is trapped While you could argue that Magnezone is uncompetitive due to its ability to abuse Ferrothorn with its fifth gen Sub+Charge Beam set, the argument mostly falls apart because, unlike Gothitelle, it needs to sacrifice important tools, such as Choice Scarf, that make it more consistent when its not trapping something. While Wobbuffet can use its fast set with Tickle and Encore to bring basically any wall into KO range for Pursuit, it sacrifices the ability to consistently combat offense in the process, and it comes at the cost of the ability to use Safeguard or Destiny Bond to improve its supportive capabilities. If it uses its bulky set, it struggles v.s. anything which doesn't have trouble with CounterCoat, and while the support it provides for sweepers is something to consider it does not guarantee victory in the same way that Gothitelle does. Dugtrio's frailness stops it from actively taking advantage of what it traps, and it struggles to break anything which isn't either extremely frail or weak to one of Earthquake or Reversal while being foiled for the most part by Stealth Rock. I could continue with Magneton and Trapinch (I think Wynaut comes under the Bulky Wobb description tbh), but you get the picture.
What I am trying to get across here is that there are six trappers which do not face the same charges as Gothitelle and Gengar do. This is where I think the idea that preventing switching isn't competitive reaches a roadblock, because as much as you try you won't find many reasons to convict Dugtrio or Magnezone of the same charges as Gothitelle beyond "it trapped and killed my Heatran/Ferrothorn", but having them available to trap Heatran and Ferrothorn contradicts the logic plugged onto Shadow Tag. The counterplay for them is the same as it is for Gothitelle (escape with a Shed Shell), yet suddenly Shadow Tag is deemed noncompetitive due to one Pokemon while they get sidelined.
Don't get me wrong: I have been waiting a long time for Gothitelle to be put on the chopping block and I hate it as much as the next guy. However, I don't personally think it has been put on at the right angle; you could say it is being cut into triangles as opposed to even slices. I personally think that trapping is a lot like Swift Swim in early BW (and, as of recently, weatherspeed as a whole in gen 5) in that there is no simple ban that actually fixes the problem in an ideal way. We could ban a specific element of it, but that would have unnecessary collateral damage as a result. My next paragraph is acting as a bit of an illustration to aid my comparison, so bare with me.
Before Alderon's proposal in BW, the problem faced was that banning Swift Swim would lead to unneccessary nerfing of weather in lower tiers, banning Drizzle would lead to a decrease in viable archetype options, banning all Pokemon with Swift Swim would lead to dumb bans like Luvidisc while also unnecessarily depriving lower tiers of certain Pokemon, and banning individual Swift Swimmers would lead to too large a pool of Pokemon being banned. A similar situation is visible with both Shadow Tag and trapping. Banning trapping abilities as a whole leads to heavy collateral damage and banning Shadow Tag leads to collateral damage and banning consistently viable and competitive Pokemon+sub-playstyles (Wobbuffet+wobboffense/wobbalance, which has enough flaws to constitute as not being noncompetitive) and banning Gothitelle and Gothorita leads to PU losing Pokemon unnecessarily (although it isn't like its losing an entire playstyle with it gone or anything, as goth is extremely mediocre in PU tbh). There is no "right" answer.
I don't want to derail the thread by discussing future suspects (I can think of something which balances Gothitelle, but I won't bring it up as that basically counts as discussing a future suspect), and I need to go somewhere - so I will just say this: merely banning Shadow Tag does not achieve the desirable outcome, while the supposedly noncompetitive aspect of trapping is contradicted by the presence of other trappers. In my opinion, there is no way of achieving a perfect fix of the problem without utilising a complex ban, much like with Baton Pass clause and Alderon's proposal. Trapping as both a strategy and mechanic is not noncompetitive, but rather the issue comes from how it is utilised and what is utilising it.
I will close out by saying this:
I personally do not think that Shadow Tag should be banned
I hope I have gotten through to at least one person, and I completely understand if you do not agree with me. I don't want to completely derail the thread with this post, so please be sensible, and thank you anyone who took the time to read this long-ass post.
