IMO, it's nasty because it's permanent. Every additional dislike just accumulates in the dislike tally for a person's profile and stigmatises the recipient: it's the intellectual equivalent of a brand or a tattoo. If it didn't accumulate in this way, I'd have no problem with it. It's not exactly like a thumbs down rating, which on most blogs only relates to specific posts and you don't know just by looking at someone's avatar that they might have received many negative ratings in the past. Much as I often disagree with Linda, I've never given her (or anyone else) a dislike rating. In the worst case, I've given people a disagree rating, because I know that doesn't accumulate and therefore doesn't stigmatise.