Most of the modern, big conspiracies have been thoroughly debunked, but that doesn't stop their spread. Any flat-earther has heard all of the flat-earth debunking. Sadly, I know a handful of flat-earthers, and I tried arguing for a while, but it does no good. Instead it appears that the theorists double-down on the conspiracy.
I think people believe in conspiracies, not because they're mislead on a certain topic, but because they want to believe. So debunking conspiracies is attacking their faith, which is what causes zealotry.
It's more like spreading a religion, which, yeah, you can't really ban it. You just have to let people do their thing.
tl;dr I agree that one shouldn't censor it, but only because it does no good.