In all honesty, a lot of people are 'hostile' in real life. However, these are the people you tend to stay away from and don't interact with.
When it comes to using the Internet, most people in More Economically Developed Countries have computers, or at least access to computers. These are almost all people you will have never met before, and so you don't know whether you'll end up falling into a crowd of people who are rude, or demeaning to others.
I personally find it difficult to react well to people who are acting 'hostile'. I only visit one other forum, but it's a place that I've been part of for over 4 years. When I see people being rude, I almost feel that it's my 'duty' to do something about it, without being rude in return, of course. The best solution, I find, is to but it across to them, quite generally, that what they are doing is wrong or at least, you are unhappy about the way they are acting.
I suppose sometimes you don't know whether these are 'full of themselves', sarcastic people genuinely trying to be nasty, or whether it's a child, not understanding what they're doing, or the consequences that their actions are having.
I tend to steer clear of chatrooms, unless it's mainly full of people I know, either in real life, or through the Internet already. Still, IM software, such as MSN and Steam Chat, are often the best way to go, rather than entering chatrooms full of people who might be waiting to take advantage of you.