To answer the original question - people can be such bastards because they dehumanize other people. For whatever reason, they don't see an individual, or a class of person, or sometimes anyone outside their own immediate gang, as a human being like themselves.

This may be because they're evil, or emotionally damaged, or lacking the connections in the brain required for empathy, or raised badly, or just immature; but people who see and rightly condemn their actions are not in a position to judge the reason for it. Dehumanizing them in turn by epithets like 'scum' and 'son of a bitch' only reinforces the them and us mentality and ultimatly leads to situations like those we see in Belfast today.

I'm not talking from any moral high ground here. I've been socked in the face twice by strangers in the street and half-strangled by a highly-strung friend. But I did something myself long ago when I was young and had less control over my temper: somebody deliberately and just for fun destroyed something he knew mattered to me and since he was only about 10, but for luck (I hit his head on grass not concrete)I might even be the ultimate pariah, a child-killer and people would be calling me 'scum' and 'son of a bitch'.

I guess what I'm trying to say is that yelling at people and reacting violently doesn't help.