Kicking people below average who intentionally are making things harder than they need to be isn't restrictive at all. They're required to clear it once and OP already has a level 80, there's no excuse.
It's not bad manners at all, actually it's behavior endorsed by SE exclusively to solve player disputes in relation to in-game content that require a party, majority rules.
If it's not trolling to queue up to a level 47 dungeon naked why is it bad manners then to kick said person? I mean if you're allowed to do it simply for the fact that you can do it what's the difference between the two?