I was a "free speech absolutist" in the early 00s, which was the "default" on places like Slashdot, and later on places like Reddit and HN. The reason I changed my opinion is that I was generally surprised by the amount of real harm that can be caused by the way technology can amplify false or harmful content. Specific examples:
1. I was actually surprised by the amount of glee people would take in online harassment, things like r/jailbait and fatpeoplehate. I believe that the social norms that would have prevented the proliferation of this content "in the real world" were ineffective in the anonymous, online world.
2. I was surprised by the amount of laughable BS that got real, widespread traction, stuff like QAnon.
3. Regardless of your politics, interference from foreign powers in democratic governments is now a much more realistic and effective attack scenario.
So I guess the short of it is that some "axioms" that I used to believe about free speech (e.g. "the truth will always bubble to the top in open debate") I no longer believe to be true in the way that technology can "hack" people's emotions. I definitely don't know what the right solution is, but I think that unfettered anonymous free speech on the Internet will lead to a type of society that scares me.