I always thought the 1st Amendment was about prohibiting "The Government" from curbing speech. I think a lot of us have gotten used to being able to say anything--things unbridled in scope and unlimited in quantity on (private company) Social Media, but such expectations are not guaranteed by Our Goverment's Constitution.
The 1st Amendment does not guarantee the right to say anything we want, anywhere we want. POTUS still has the absolute right to walk around the sidewalks of DC and spout whatever non-sense he so chooses.
If I go to Walmart and choose to shop in my underwear, they have the authority to make me leave and escalate to authorities if I deny their order. To me, our current laws put us in the same position with speech on Twitter. Our current laws allow private business to make up whatever rules, restrict whatever they want. It's their platform their rules.
I'm suggesting we need a company who makes it their business to allow content and protect their users using the actual law. US law shields content companies from liability because of what their users publish and upload. If someone uploads CP to Reddit then it's not Reddit that's punished (assuming they made good-faith attempts to remove the illegal material).
AFAIK, the users on Parler did not write anything illegal. Maybe they did - idk for sure. The messages on Parler were purely grotesquesand someone didn't like it.
Social media has given humans the once-unthinkable capacity to influence behavior and discourse across the world in real time. Our laws in the US have not yet caught up with this still relatively newfound tool.