It's the practical erosion of Free Speech. Liberal (small "l" liberal) democracy and liberal science thrives on members: 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…
The censorship and punishment you claim as new is plainly and obviously not a recent development, look at how socialist and capitalist ideas have been treated for the last century. Or how American evangelism has treated "dangerous" ideas for even longer than that. https://www.amazon.com/Scandal-Evangelical-Mind-Mark-Noll/dp... , for instance. Never have we been a country full of people willing to admit we're wrong. But we're increasingly a country of people being pandered to by those who want to make a buck telling us we're not actually wrong.
I think you'd more easily make the OPPOSITE argument, that our norms about what is acceptable speech have eroded too far, that we've taken free speech to an unhealthy extreme (such as how our tech platforms will happily amplify the speech of extremists - in fact, they PREFER to do this, because their algorithms have figured out that it gets more ad views).
If it's acceptable for politicians to respond to losing popularity by claiming fraud - as Trump has been doing for months - then you are on the path that leads here. If the resulting violence is not acceptable, but you ALSO don't want to restrict Trump's speech with stronger norms, what do you propose instead?
How many previous presidents would be inciting this sort of thing? How is that the result of less free speech?