Social media platforms are content-neutral. They want to be treated like the "public square" because a lot of benefits come along with that. But then at the same time, they censor content that they disagree with. That's where it crosses the line. If Twitter came out tomorrow and declared that they are officially a left-wing social network and updated their rules to reflect that, then I'd have no problem with them kicking every Republican off the platform and banning every person who complained about taxes being too high. But Twitter won't do that.
I don't want to get further off on the tangent about telecommunications infrastructure, so I'll just leave that alone.