You can find a happy medium, allowing all but the most egregious things. Human judgement isn't perfect, but it's good enough, because ban-worthy content is relatively rare. Freedom of speech is like personal liberty: Do what you want without harming others.

Want to talk politics from a moderate, conservative, liberal, socialist, or libertarian perspective? Sure. But advocating violent revolution is something different.

There's a lot of room between a totalitarian Ministry of Thought and enabling actively harmful extremism.