“However, there are a few web sites with billionaire owners who have a de facto monopoly over speech—they “own” the public square.”
You post freely on FR; though, the mods may delete one of your comments if it does not comply with TOS. That is FR’s right. There are other web sites like FR. You can post to your heart’s content. You are not limited to Facebook or Twitter or You Tube, etc.
You are missing the forest from the trees.
I suggest you carefully read the Sherman anti-trust act.