The remedy is to break up the big forums, not to take away the rights of their owners.
Why not? We have granted ourselves the right to limit the rights of corporations.
The individual owners can keep their individual rights.
You have to remember that "corporation" can mean any group organized for a purpose. It can be Exxon, but it can also be Planned Parenthood or AARP.
People who can't speak loudly enough by themselves have a right to organize into a corporation, pool their money, and speak loudly together.
You can argue that a business should not be both a commercial enterprise and a holder of 1st Amendment rights, but that's not what the law says. And anyway, it would be an impossible line to draw.
Correct me if I'm wrong, but isn't forbidding them from censoring user content orthogonal to this?
Human rights, however, are natural rights.
I was responding narrowly about the idea that "free speech" demands that the US govt can force companies to choose what to publish.
Forcing a company to stop operating here is an entirely different concept.