1. Being willing to admit they may be wrong
2. Having access to a diverse information diet
But the past two decades have shown erosion of not only legal Free Speech, but practical free speech:
* Whereas previously they were just ignored (or even rebutted), today employees, students, and professors are all punished administratively for saying something that contradicts the narrative of the predominant members, or that may be offensive to someone. "If the federal government won't do it, let's restrict free speech on the ground-level."
* It is difficult to broaden your information diet, even intentionally. The platforms of yore that provided a place for free debate are empty, with everyone having migrated to social media where they can form disjoint sets defined by their ideology. Ever try having a dialectic on Twitter with someone of an opposing ideology? Haha, good luck.
* Expanding on ^, folks that aren't actively seeking diversity of thought have no natural avenue of exposure to information that contradicts their ideology. Whatever information delivery mechanism they choose today is, by default, going to agree with them.
* All of the above results in: staunchly maintaining your correctness in the face of opposition is rewarded far more strongly than admitting the possibility of wrongness
* Online radicalization makes in-person dialogue even harder; there are fewer and fewer opportunities for two moderates to debate when the possible participants are further across the spectrum than ever
Although restricting offensive speech has the upfront benefit of not hurting our iddly-widdly-fweelings, this is the price we pay for abandoning free speech.
For further reading, I recommend Kindly Inquisitors: The New Attacks on Free Thought [0]
[0] https://www.goodreads.com/book/show/703086.Kindly_Inquisitor...