Well, think again. That's the rub. It's a bait and switch maneuver. The smut-censors say they're going after porn, but they quietly restrict political speech. CyberPatrol bans animal rights web sites - Part 2 In which the general connections betwen labeling and censorship are discussed.
Much attention is given to establishing that government censorship is involved here.
Some philosophical fallout, included for completeness. That's enough to get it on the blacklist. Books are dangerous, you know. They can cause people to question authority. They've never actually explained how this happened.