It doesn't seem any more wrong than confinement or banning
Well, if someone is confined, they can still read other people's posts, can't they? If they're banned, then I assume they're banned for breach of rules. But being forced to ignore someone could potentially lead to a situation where a poster could say just about anything about another poster, and because that person is forced to ignore, and everyone else is ignoring anyway, then some real attacks could go unnoticed.
I think that the main objection I have to it is that it's a sort of a 'nanny board' thing. We are all, I believe, adults. This would seem too like separating naughty children because they can't decide who stole who's chocolate bar.