If anything, the first amendment explicitly protects a private organization's right to curate their own platforms the way they see fit.

Twitter could declare support of Donald Trump a bannable offense today, and those people can promptly sign up for a site like Parler.

And Parler has even more censorship. Adult work is completely legal in the US, and pornography is a form of constitutionally protected free speech, yet Parler strictly prohibits it on "Decency" grounds.

I see no problem with social netoworks drawing a line in the sand. The big ones can draw a line at violence, hatred, and fascism. The little ones can draw the same line and stand shamefully on the other side.

And nobody loses their right to speak.