I see it so often. Someone will start a thread which is a little bit dodgy (e.g the jordan one this morning - this is not a thread about that thread in particular, that's just a recent example)and one or two people will say "oh yes, I agree" and have a bit of a laugh and then a poster with the opposite opinion will say "Oi, that's not nice, don't say that, you are a freak etc..." there will then often follow a spate of similar posts all disagreeing with the op.
Why? Surely it can't be coincidenec that all the posters who take the opposite view suddenly all open the thread together. Are people guilty of not wanting to be the first to have a go, and then piling in when they see someone else has.