What you're referring to is the codified freedom of speech protection in the Constitution. That's not what I'm referring to.
My post is about the ideal of freedom of speech. There is a debate to be had about the level to which "platforms" should respect that ideal. My position is that relying on the good faith of platforms to moderate speech is dangerous when those platforms are as dominant as Facebook/Twitter/Google are.
So you see this is separate from Article I.
Nowhere did I say that the government should do anything to this pile of fascist idiots over at Parler. I'm just saying that a social network predicated on the idea of "we will never moderate our platform" will be an actual legitimate trash fire of a place to spend time.
Moderation is not censorship. If you're being moderated at a particular community, it means that the community thinks you're offensive and don't want to hear from you anymore.