In fact, 5% – 18% of Slashdot moderators have been banned. Follow the link above, and you will encounter a research paper of a banned Slashdot moderator, who concludes “Slashdot stands as an example of a best-of-breed solution for those who wish to create a community that promotes agreement” – agreement, of course, with the editors.
After I gained moderating privileges on Slashdot once again, I stumbled upon an interesting sig that indicated that Slashdot editors exercise censorship.