Wikimedia draws a disproportionate number of two types of people: those with some antisocial tendencies, and those with an unusual belief in various notions of "freedom." People being people, anyone in both groups will tend to use the second trait to reinforce the first. We've developed the basics of a legal system and a convoluted set of policies on the English 'pedia to attempt to address this particular problem, but as most know we're a ways from doing that well. Some folks are convinced that their rights to a forum require others to accommodate them; because they're clods and don't respond to social pressure, most eventually vote with their metaphorical feet.
Nathan