There isn't a black and white answer to this. It should be painfully obvious by now that unrestricted free speech also enables incredibly technologically amplified propagandists of various stripes to drive people's behavior to various extremes including threatening the existence of that same democracy.
Yes, there is certainly a limit on both sides. I think when social media platforms would ban hate speech and the like, most people were perfectly ok with it. Once they started banning political opinions that most people would consider not that inflammatory, or even interesting (think COVID discussion) people starting having a problem. The social media platforms themselves became a political tool rather than a tool to share ideas.
Why is Twitter really important? This is really the crux of it for me. Ever since mass communications, the news was the arbitrator of opinion. It was common for journalists of prominent newspapers (like the NYT) to declare themselves "kingmakers" in elections, even presidential ones. How they portrayed a candidate directly affected his or her outcome in a significant way. If journalists at the NYT thought a candidate wasn't a "serious candidate", they wouldn't get much coverage, or that coverage would be intentionally unflattering. Social media breaks that barrier down because now the politicians can circumvent the news as a middleman of information and we can now have discussions of ideas on a fairly large scale without requiring the news to deliver that information.
Once Twitter becomes just another arbitrator of information, then we've regressed as a society back to the times where all our information was filtered by "kingmakers." Instead of a new world with much more available contact with our political class, we digress to the way it was before, the only difference is we have new arbitrators.
