Do you really think people at large didn't know about hanging, slavery, human sacrifice, and ideas about a flat earth in societies where these ideas were applicable?
stevebmark said "I've never seen a bad or immoral or harmful idea die out when more people learn about it and scrutinize it"
So I gave examples of some ideas that did in fact die out when people learned about them and scrutinized them. My argument was that it's naive to think censoring ideas this time will be on the right side of history.
Then suddenly there were factories who would hire anybody who showed up and pay them real money and plantation workers started running off to work in the factories left and right. It was no longer that people stayed because they had no better option, they were then being forced to stay against their will. The dynamic changed. Chains and beatings entered the scene to keep slaves from running off. They did anyway, so their replacements had to be forcefully kidnapped because there were no longer any volunteers.
The whole thing collapsed and was dismantled in a relatively short period of time after that.
There's no natural inclination of humans towards justice or injustice, beyond the limits of our own psychology. To me, the idea that there is some internal teleology towards justice is absurd. These are material struggles and material gains that must be defended materially.
We should reject this kind of naive idealism.
It seems that having free speech is a necessary, although not sufficient, condition to improve society. It's a principle worth defending.
My opposition to censorship derives from the fact that it tends to require an unjustified hierarchy (i.e. the violence of the state).
However, I have a real problem with imparting some kind of magical quality to ideas. I'm particularly annoyed by the way in which free speech advocates act like social norms are a form of censorship. More specifically, that free speech requires platforming -- i.e., rejecting a freedom of association.
While I do think that the power companies like Google exert of society is well wroth investigating, in general I find that these are much weaker examples of the use of force to censor ideas.