I'm sure you've met people who, in normal daily life, are more aggressive and combative than others. The joy of competition stems from the desire to be superior to others - its part of what defines ambition and makes the world go round. The extent to which people need to also humiliate and demoralize their competition is a function of the person in particular. Its possible there's simply a "douchebag gene" or maybe its tied to testosterone or whatever. Point is though, its human nature and unavoidable in any public community. People probably do not consciously recognize how much social consequences influence their behavior but they certainly do, hence the anonymity of the internet exacerbates this sort of thing.