So, case in point: the alleged censorship of conservatives by social media. It is an article of faith among many conservatives (religious and social, responsible as well as crazy) that Big Tech is trying to shut them down, exclude their voices. Big Tech and its apologists say, Nonsense, we're just trying to keep things safe and civil on our platform(s). (Leaving aside whether they actually do this consistently, it's a plausible defense of their actions.) And when the conservatives claim censorship, the apologists for Big Tech say, Nonsense, the Constitution only prohibits the government from censorship; private companies can do what they like. Again, plausible enough.
But let's look at this another way. Shopping malls have been around for a long time now. They differ, however, in a significant way from the stores on the street: they exclude certain forms of communication. The mall as a whole, including its parking area, is a commercial enterprise. All communications within the mall area must be approved by the mall. Not only can you not hand out flyers advertising some other store's goods on mall property (the stores in the mall pay for the advantage of not allowing their competitors on site to make comparisons), you can't solicit for charities or advertise community events or even stage a high school football parade on site without prior permission from the mall's operators. All communication on mall property is under prior restraint by the mall, period.
Now, you can say, Well, build your own. And competing stores do. But what would happen if malls became so ubiquitous that it wasn't economically viable to build a competing store in some town because there were three or four malls that had sewn up the territory? Not only that, but all the malls were owned and operated by the same holding company, or by holding companies with interlocking boards of directors? Not only would that seriously impact economic competition, creating a near-monopoly on certain forms of commerce, it could also create a very hostile environment for certain community good causes. What Big Mall doesn't like can't get promoted -- which might not be terrible if that applies to all causes, but if there are some causes that Big Mall does like, and promotes, does that not handicap other messages?
We all accept shopping centers' restrictions because there is always meaningful competition among possible hosts for what we're trying to do (sell Boy Scout popcorn/Girl Scout cookies, promote blood drives, hold community rallies, put up notices on bulletin boards . . .). If the mall won't let you promote what you want there, Harrison Hardware or Fred's Market will. But what happens when there are no longer meaningful alternatives to the platforms of Big Mall?
Restraint of trade is an issue, even when government is not involved. And UN-official censorship by social consensus can be as stifling as official censorship. Both have usually been considered un-American, although I admit that the ideas exist in tension. Market competition means some companies out-compete other companies; however, government breaking up monopolies and cartels is not a radical idea. Likewise, some ideas offend against the social consensus; nevertheless, stifling those voices has usually been seen as a bad idea.
I never had any interest in Parler. For that matter, I've never had a Twitter or Instagram account. I started out here on LiveJournal, because I liked its mechanics. I only opened a Facebook account to keep up with people I knew who didn't do LJ. Eventually, all the eyeballs drifted over to FB, and that is now the primary place where I keep in touch with people. But I still do LJ, because it is built for long-form blogging, which is what I do. I don't feel the pressure of viewpoint discrimination personally, but I have friends who do. And as someone who wants all ideas fully discussed so that truth can emerge, I am on the side of free expression. When we drive people underground, we only make their communication uglier and crazier. Sunlight is the best disinfectant.