There are plenty of people that cheerfully post extreme opinions, even under their own names on Facebook. I get the impression that these people are some combination of: reckless/impulsive, in a social bubble, "got nothing to lose", or not very careful thinkers. I think that the effect of more careful and cautious thinkers self-selecting out of the conversation is often just to make the conversation dominated by the above sorts of people, and I don't think that's an improvement.