The irony of the internet. The internet connects people easily and quickly. This means that someone can access the world from their desktop. It also means the world can access them.
Unfortunately, not everyone in the world is nice. Even bigger problem - not everyone in the world could possibly share the same opinions. Couple this with the anonymity that people feel on the 'net and you have a recipe for disaster. Radical thinkers try desperately to influence the thoughts of less radical people. Hatred grows as people adopt the pack mentality, and many people are naively swept along for the ride.
One of the fundamental failings of any text based system, is the lack of an ability to portray emotion or expression well. This means that people quickly misinterpret other peoples writings (posts, blogs etc). Add to this the fact that many people are trying to communicate using a language other than their native tongue and we have trouble brewing. Sarcasm really doesn't work on the internet, and causes rage. People fly off the handle when their opinion is challenged - even though the challenge is purely in their perception (I have, in another life, reacted badly to a posted response to something I wrote, only to realise days later the OP was probably agreeing with me). Forums and social networking are bad news in the wrong hands. Technical forums seem to be the worst - where some experts take it personally when people don't share their view (Open Source vs Commercial, UNIX vs Windows, PC vs MAC, c/c++/c# vs Java (don't even mention VB)).
Unfortunately (and ironically) even outside the internet, it is our differences that make the world a wonderful place. The world would be boring if everyone was like me - yet somehow I get sucked into the perpetual attempt to try to convert everyone to my way of thinking (which always causes nice fireworks - I was brought up Catholic, so I disagree with everyone). Worse still, people seem to feel as though they absolutely have to share their views with people whose opinions will never sway. There are people that will believe in Global Warming no matter what, and there are people who won't - no matter what. Often upbringing plays a large role in our attitudes and beliefs - whether obviously through culture, or less obviously through watching and learning from our parents.
People also tend to remember negative more than positive. In fact, our media exists on this premise. Car accidents, burglaries, war etc all make the news daily. If there were no car accidents today, how many news agencies would report on it? Peace sometimes briefly makes the news, but it is rarely (except in major conflicts) headline news - yet small armed conflicts and riots fill even the ads for news. I suppose because good is usually the 'status quo' we don't really care about it. If I play football (Aussie Rules, of course) I remember if someone hits me or breaks my nose, but I am unlikely to remember people who play fairer than the average opponent.
Short story: Humans get very attached to ideas. The fact that some people like NRL has absolutely no affect on my life. The fact that I like AFL has absolutely no bearing on theirs. Yet so often people will argue (seemingly to the death) that one is somehow better than the other. The world is a wonderful place because of it's diversity. The world is also a terrible, evil place because of it's diversity. Diversity makes life what it is, yet while we love small difference, we get frightened by people who have radically different views to our own. And people still use VB?