> platforms of a size large enough to justify treating them as a "public square" must meet common-carrier-like requirements that prevent them from discriminating based on viewpoint.

This sounds so reasonable and nuanced until you reach this final phrase: "prevent them from discriminating based on viewpoint." Doing that requires the state to determine what speech is "un-biased, politically neutral speech" and which speech has a political "viewpoint." And under this law a government will determine this at the point of a gun, not the people operating individual websites.

(Because obviously if you implemented this in a truly content-neutral way along the lines that you suggest for a common carrier, every platform would be overrun by spam. So there has to be a decision about what constitutes biased speech, and that means political figures will be making determinations.)

This isn't theoretical. Nobody in this country even agrees on what "political/biased" speech is. Things that used to be broadly accepted by our whole society no longer are. I'm not going to go into examples, but you know exactly what they are. And you probably disagree with half of them. This law means that you won't get to decide, the state and the courts will.

If your problem is the over-concentration of social networking companies, I'm happy to agree. I urge you to support laws that reduce the power and userbase of these firms in a content-neutral way -- without placing the government in charge of what speech is "ok".