The XP system, along with the site's other features, has actually done well to make this a community of users who care — about the quality of their posts, their reputation, even each other. Being a user here is more fun, and it's less anonymous than reddit. This encourages and rewards good behavior, and makes misbehaving a truly stupid option.

Lurkers will lurk, and everyone is fine with that. They don't care whether there's an XP system or not, but there are many users who like it.