A perfect storm of factors come together to engender the rudeness and aggression seen in the comments’ sections of Web pages.

First, commenters are often virtually anonymous, and thus, unaccountable for their rudeness. Second, they are at a distance from the target of their anger — be it the article they’re commenting on or another comment on that article — and people tend to antagonize distant abstractions more easily than living, breathing interlocutors. Third, it’s easier to be nasty in writing than in speech, hence the now somewhat outmoded practice of leaving angry notes

via Why Is Everyone on the Internet So Angry?: Scientific American.