1)
Seen here (thanks Roo), it becomes more than a simple coin flip after one turn and can very well be played with to make it last several turns without getting hit in return (and even if you do, the initial turn is, again, completely luck-based), i.e. Substitute and Thunder Wave. Assuming, because the chance gets higher and higher that eventually you will hit yourself at least once, you do lose a turn, their free sub is up and then you either get Thunder Wave'd (depending on the set used) further hampering your ability to fight back, or hammered with your own +2 attack using Foul Play. The only way this could be any more subjectively infuriating is if Klefki had anything more than Leftovers to heal itself with. It's mindless and if anyone decided they wanted to use it wouldn't be hard to. THAT is the argument behind banning it, as far as I can tell, and it's the reason I suggested banning more than just Swagger alone, as by itself it's not too overwhelming.
2) I think I went over most of that already so,
3) Basically what I said with the other post- we can probably limit it somehow without outright banning one thing entirely
Your point is noted, but none of those are nearly as likely to occur as Confusion is. Paralysis, while it doesn't wear off, is only a 25% chance each turn, and there are a considerable number of options to avoid it (Electric types are completely immune; most Ground types are as well; Limber is a thing in the same vein as Own Tempo if anyone wants to use that argument) as compared to Confusion having Own Tempo and... switching. Sleep moves sans Spore are generally inaccurate and if one thing is asleep nothing else can be put to sleep as well- unless you're not using Sleep clause, but that's neither here nor there. No move has any higher than a 10% chance to freeze something (excluding Secret Power for obvious reasons). Crits were nerfed this gen as it is, and, without a set dedicated to it, are only a 6.25% chance which is less likely than anything mentioned here. Even then, the only Pokemon that can reasonably dedicate itself to 100% crit is Kingdra and you're not going to sweep a team with 85 speed.
EDIT: and in the time I took to write this there's been like four new replies so if anything was already addressed don't mind me
EDIT2: after reading the replies I realise there would basically be no use for Swagger if we removed the combinations that make it into abuse cases, so with that said maybe we can just get rid of it altogether after all, idk