but I'd propose that maybe unstable people who hurt people based on what they read are kind of inevitably going to end up on that trajectory regardless of the freedom of our speech spaces

You say that, but do you have any evidence for it? Are we just going to brush off the mentally unwell people that cults like QAnon prey upon as being a lost cause? As being people who would just be violent because the seeds of sin in their souls compel them to? You're just arguing for a secularized version of Calvinism that is even more reliant on faith because it lacks the element of theological reasoning.

And that maybe it's not worth sacrificing the free speech of all people simply because a few people are going to do bad things

Maybe this obfuscates relevant factors, like how money controls media and it's not just a matter of private citizens vs other private citizens.

What you're describing where people end up in their own media bubble is exactly why we need more open access to speech

It takes more of an argument than you have so far put forward to prove this, though I agree with you in a way that I suspect you would reject. Specifically, the blackballing of journalists and other sources who provide more useful explanations than exist in mainstream American Discourse is definitely part of the reason people resort to cults.

That said, if we are discounting questions like Class consciousness, your thesis falls apart entirely. These bubbles are largely self-selecting, based on marketing algorithms for the consumer-lifestyle brands that you call American politics. There is nothing stopping a brain-rotted Twitter Q freak from going on some socdem hive on Reddit, but they don't want to and they have been encouraged to this mindset by various forms of conditioning on the multi-billion dollar skinner boxes that are social media platforms. Of course, there are less polarized spaces and ones designed for "open debate" (and again Reddit provides an excellent example of these empty gestures) but overwhelmingly what we see there is more tribalism, just with a different set of etiquette.

This shows one of the many significant failures of idealist fetishization of open society: People only have so much time and effort to put into research, especially more nebulous ideological subjects. Ideology is first and foremost a survival strategy, and people will budget their finite resources based on what they are able to project as best serving them from the limited information they operate within, starting from environments that are overwhelmingly controlled by the rich in neoliberal societies. You already have your goddam Marketplace of Idea and it has failed.

free, neutral platforms for people to have these kinds of discussions on.

Neutrality doesn't exist and the bodies that claim to be neutral are just question-begging their own ideology.

Some people used to think that the internet would end war, but they were operating on a type of idealism similar to your own.