How do you know that something is extreme if you can't hear it? How do you engage individuals, hopefully productively, if you don't allow them to speak?

If the answer is social norms, how do you prevent those norms from drifting overtime into authoritarianism? Start small, attack only the extremists. Then slowly turn your forces against your opposition. This is the kind of thought that Pastor Martin Niemöller wrote about in "First they came...." Notice that historically that poem applied to Germany and even Estonia and Australia. These countries were or seem to be morphing into an authoritarian state.

Edit spelling