If some potentially powerful ideas were suppressed successfully, we wouldn’t know about them, would we? Seeing only the cases where censorship failed, we may underestimate its impact.
Second, ideas can be killed without being completely erased. For example, you can read on Wikipedia about the Cathar religion, but how many active Cathars do you know? The crusade was a success.
Third, driving an idea into underground can harm its development. If posts are getting deleted, you can’t have the three levels of response (can’t find a link now, but the idea is that quality debate requires at least: someone stating a hypothesis, an opponent refuting it, the original author explaining why the refutation was wrong, and the opponent explaining why the author’s objection was wrong). If adherents can’t build their reputations, it is hard to distinguish in a debate between actual believers, trolls, and false flag operations; there is no common knowledge of what the idea actually is (so everyone is free to replace it with a strawman).
Here you go: four layers of intellectual conversation.
Would be good to have it as a tag/wiki page
All your points are correct, but they explain why censorship can be successful, which I don’t doubt. My point was that it ends up not being for the greater good.