If it was a question of taking simple offense to something then I would say yes, flagging is a form of censorship. However, no one who does not want to see a very ugly vag and giant diseased c**k, at any time, especially now while consuming porridge, should not have to see even a thumbnail of that. There should be some option to have this stuff shunted well.

In the case you mention, the poster was deceitful, in that the pornographic aspects of the post were meant shock and surprise ... as @hilarski mentioned, if proper flagging and title warning was used, one could simply avoid .. even MUTE the poster so they can be bypassed in the future. If deceit is used to draw people into a post with no such warnings, then they should be flagged into oblivion imho.