All of that is sadly true and it's a fundamental problem with humanity. I'd say that the only solution I am seeing is that the managers must proactively shut down the extremists early and hard.

If you demonstrate that you will not submit to extremists, I've found that a good chunk of the more balanced people are then encouraged to speak up.

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TL;DR: Silence the bad and loud voices, and the wiser and quieter voices will start speaking.