The problem is that the tech companies produce an extremely distorted "marketplace", one in which there is little reason to believe that the process of interaction will lead towards greater understanding and correctness instead of greater bigotry and confusion.

There are three factors that lead to a poor information marketplace--like a real marketplace that is full of nepotism and dishonesty. Censorship and official fact-checking solves none of these, and aren't a very good band-aid either, but it's conceivable that they're better than the status quo.

The three factors are:

(1) Echo chambering. People enjoy interacting with "their people". People also enjoy eating sweets. The problem is that social media makes it so easy to find and interact in a positive way with almost exclusively one's own people that what once was a nice treat has turned into an unhealthy overconsumption of mostly empty cognitive calories that are bad for your intellectual teeth and lead to intellectual-diversity resistance. Some of these chambers develop (or are manipulated) in more profoundly harmful ways than others, but they're all bad for an actual marketplace. If everyone has to go to their own church's market, the diversity and price structure of products is going to be limited and expensive compared to if shopping is relatively open.

(2) The right to you-shut-up instead of the right to reply. In order to reduce genuinely problematic behavior (harassment, etc.), most services have fairly extensive blocking capabilities, which when employed against people whose arguments you don't like, means that you get to say whatever you want to whoever will listen to you and you can actively prevent the alternative from being viewed. Nobody really has a great answer to this, and Apple and Google's stores insist on some sort of blocking feature. X has made one attempt at getting around this by making it so if you block someone else, you can't see them, but they can still see you. That's...something. But you can still curate a community of unchallenged lies on X by blocking everyone who has a different perspective; the only difference is the people who know they are lies get to see you lying. But they can't do anything about it. It's still analogous to vendor lock-in, which is a marketplace distortion that generally results in bad products.

(3) Anarchic lawlessness. Physical marketplaces are vulnerable to various sorts of exploitation, including outright thievery and lying about products and then skipping town after duping a bunch of people. We have, therefore, come up with a set of ground-rules enforced by law that curtail the exploits and thereby enable a working marketplace. The online versions that attempt to overcome anarchic lawlessness look like haphazardly-applied reactionary vigilantism with sanctioned cruel and unusual punishment: banning, shadow-banning, cancel culture, etc.. But that the solutions are poor thus far does not mean that the problem isn't there. People can and do say things in a compelling way that are, nonetheless, flat-out false and done for personal gain; and they can do this in ways that they're unlikely to be held accountable for. You can't sell contaminated food to kids, but you can post a bunch of addictive attention-crippling product-opening videos for kids. We need to figure out ways to have the analog of a system of laws, because various sorts of human societies do not necessarily work out purely on the basis of natural dynamics. Often they need some help to be pushed into the regime where the rules of the game reward pro-social behavior. Once the game is good, then you can be hands-off and let people play it.

So it's sensible for liberals, and everyone, really, to be very very worried about tech companies' impact on the marketplace of ideas. But we need to take more to heart the lessons of society where we expect that anything we put into place to solve a problem will almost surely be used abusively as badly as it possibly can, and devise things where the worst practical abuses are clearly far less bad than the problems they were supposed to address.