I don't think censorship really has much to do with copyright. A book can certainly be in public domain, and still be censored.
It is mostly about infringing the restricting the ability of individuals to choose what they would like to read, hear, and watch; and also infringing their right to free expression.
:-) On the topic of the book by he-who-must-not-be-named, I beg to differ. The intention is quite clear, copyright is just the means to achieve it.
Here is a Gedankenexperiment: assume that there is a jurisdiction in which the state, instead of the estate [1], automatically becomes the copyright holder after the author of a work passes away. [2] If the state starts making rules on which books by dead authors cannot be published, wouldn't you call it censorship?
[1]: Sorry for the a-maize-ingly corny and unfunny dad joke, couldn't resist.
[2]: This is not too far fetched, apparently this is roughly what has happened with you-know-what in Bavaria.