I think what Eugine_Nier meant is that people who already have an interest in controlling other's ideas are morelikely to seek out office in an autocratic government,

Eugine_Nier should then communicate more clearly what he meant.

And this wouldn't explain why hereditary absolute monarchs that did NOT seek out office are also likely to censor and control speech.

as opposed to autocracy having some magical corrupting nature that makes people want to engage in arbitrary censorship.

Nothing magic here, I believe people wanting influence over other people's thought-processes is a part of human nature. When people can fully satisfy physical wants, influencing how other people think becomes their main goal then. When they're movie-makers, they make movies. When they're philosophers, they write papers, When they're autocrats, they send their secret agencies against dissenters.