Ask HN: Why are people so unkind (on the Internet)?

It seems to me that some people tend to be more critical, abusive, etc on the Internet than in 'real life'? I can't imagine that these people would say the kinds of things in person or over the phone that they say on discussion forums or in some of the support tickets/emails I've seen over the years. Is it the perception of anonymity or lack of physical contact (with the people they're corresponding with) that causes some people to disregard social conventions or to abandon common courtesy towards others? Or am I wrong in thinking that the Internet makes any difference to these people?