Pretty soon there are news reports about how badly you discriminate against certain groups and world governments start poking their nose in your business. Plus you hit that endless stream of edge cases where no matter what solution you choose someone is going to compare it to the holocaust. Even clear simple policies get bogged down in edge cases extremely quickly. For example, you might have a "no nudity" rule on your site. Very easy, but now you're getting lawsuits from the breastfeeding mother's association on one end for taking down their content and the anti-pornography league on the other end because you allowed a picture of a bare ankle to remain up.