Free speech is also a technological (or lack thereof) outcome. In 1700s, if you had a misguided evil thought, your chance of realizing full effect was still low because your thought must travel through multiple hops, each hop evaluating your idea and possibly terminating the propagation with some probability. So in societies without technological advancements, bad ideas and their damaging effects can stay contained in small groups. But what if technology can directly inject any bad ideas to entire population all at once instantly? Is free speech still viable or do we need new philosophical principals on human communication?

The often left unsaid basis of free speech is that each member of the audience is capable of rationality evaluating the argument, willing to invest in fact checking and is educated on background material. When these conditions are not satisfied, there will be members of audience who will make suboptimal choices based on misinformation with some probability. When scale of audience becomes large, even small probability can uproot sane society.

All these are very interesting questions and honestly I don't think anyone has answers.