And insofar as First Amendment law is concerned, the "fire in a crowded theater" never held legal weight whatsoever and is a poor example of the guardrails that restrict freedom of speech in America. The Brandenburg Test is the current accepted set of guidelines to determine whether speech falls foul of the First Amendment.
In any case, confirmation bias is a simple fact of human nature. We readily accept things that confirm what we already believe or want to believe, and we reject anything that clashes with those beliefs. You're correct that most people exist in a comfortable bubble where their assumptions and beliefs are never challenged. This is a general societal problem and not one that afflicts just one side of the political aisle.
The only way to combat the rising tide of bullshit is to get out there in the trenches and have the debate. Get our message out there, even if it means getting into an ideological brawl. When we disengage out of frustration, all we're doing is ceding the battlefield to the enemy and allowing them to claim an unearned victory.
Restricting and punishing speech is the tool of tyrants and has been throughout history. I don't know if this particular form of societal herpes can be cured, but I know for damn sure that embracing tyranny of thought isn't how to go about it. Tyrion Lannister had it right when he said that tearing out someone's tongue doesn't prove them a liar, it only proves that you're afraid of what they might say.
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