Actually, lefties benefit a SV/SC mon more... but alas, I drift off. I'll try to make an overview of the discussion, for as far as possible.
Arguments pro evasion ban
1: Evasion can decide matches by giving a pokemon a free turn, for which he has to do nothing.
2: Evasion overcentralizes
3: Evasion cannot be countered within the meta
4: Evasion lets our opponent decide how accurate our moves are, as opposed to we deciding it ourselves; If I use Ice Beam for the 100% hit-rate, I want it to hit 100%.
5: Evasion lets luck dominate skill.
6: Substitute can basically multiply the chances of dodging an attack, hereby increasing the evasion that much more for free.
These arguments were (besides flaming and ad hominems) responded to by
1: The pokemon that have Snow Cloak / Sand Veil as abilities generally do not have enough power to be able to decide a match with 1 free turn, and it is not even that likely to get that free turn. In the case of evasion items, the chance of it happening is smaller than that of one of the 100acc/90pow moves statusing, which can decide a match just as well (imagine a starmie Ice Beam freezing your Tentacruel)
2: If evasion would overcentralize, why is it not there already? It's available in many forms and ways, yet no-one really uses it.
3: In the case of abilities, weather changing does that, other than that, Machamp and infinite accuracy moves do that. Just hitting hard might very well work as well.
4: But there is so much decided by your opponent... Evasion is just one of many things. @ the 100% rate: You'll want it to OHKO Salamence with Hidden Power Ice, too, but he can run Yache to survive. You can't determine everything in a pokemon game.
5: It doesn't, as the luck will only kick in in a small amount of games, even on a team that's built to abuse it.
6: The odds of missing a 100% accuracy attack vs a pokemon with BrightPowder setting up 5 substitutes are 41%. So, in 41% of the cases, a pokemon will be at 1% health with a free substitute, and (in all but 8% of the cases) no boosts. That's not a gamebreaking advantage at all..
Sub+Lefties+SV/SC is a bit more obscene though, with 41% chance of getting one free turn, and 26% chance of getting one more. The thing here is that in current OU there are no pokemon that can reliably abuse these free turns, as the SV pokemon (Gliscor, Cacturne) are pretty easily walled when using a SubSD set, and the SC set rely on hail in the first place, which is hard to keep up, and are quite easily countered as well (Froslass, Glaceon, Beartic)
Arguments contra ban of evasion in any way:
1: It's a non-significant portion of the metagame. (in a generous estimate 6,7% of the teams use it, and in a more generous estimate, <1% of matches are decided by it as shown
here)
2: It hurts the metagame more than it benefits it.
3: Luck is part of the game, and as such, so is evasion.
4: Only things that are truly broken, that the metagame has no way to deal with, should be banned, and evasion is not one of them.
5: There are many more ways of hax (HaxRachi, FlinchKiss, Quick Claw, Focus Band), why ban this one and not ban those others?
Responded to by: (again, disregarding flaming and other happiness)
1: It may not be a big portion, but if it decides 1% of my matches, that's 1% too much (4% has been falsely thrown around here, but that's irrelevant)
2: It lets luck take over over skill, which is something unwanted in the metagame. The "banning" of Froslass, Sandslash, Cacturne and friends on their respective weather teams is collateral damage and not more hurting than the hax on them is (refer to argument 5 pro)
3: Luck currently is part of the game, but we can't do anything about most of the luck, i.e. critical hits. This is part of luck we can combat, and as we should minimalize luck, we should combat.
4: I didn't read any real arguments against this so far, besides from perhaps strawmanning that evasion
is broken, the metagame just hasn't figured out yet.
5: Irrelevant, we're talking about evasion now.
I believe I caught the most of it as neutral as possible. Had I missed something, I'd be glad to edit it in if pointed out in a not ad-hominem way. I suggest y'all stop flaming at eachother for having different opinions, either way. Deal with the argument, not the person argumenting.