I think it should be allowed to take a moral stand, which is why your freedom of speech has nothing to do with social media and I'm glad about it as well.
Those laws are relatively recent. By your very own argument, doing all those things was perfectly A-OK before the laws that barred discrimination went into place. Oops.
What recourse does the average citizen have to abuse from these entities? Think of all the ways Google or Facebook could screw you over or even shape the social/political narrative. This should be a free-for-all?
"Just build your own global social platform"... yea, not possible. In the mean time, they can abuse their power while you get up and running, or never do.
Think of it another way. If the government is constrained, but massive corporations (who pay off politicians) aren't, doesn't this clearly seem an end-around for "government" to encourage private companies to do the censorship they want, enact favorable policies for them in return, and the powerless individual, or small groups suffer similar consequences as if the government themselves censored them? It's an easy hack for the 1st amendment.
I wonder what happened to antitrust law enforcement in USA.
It is legal, due to the first amendment, but it sure does say a lot about you as a person.