this is censorship, which twitter is allowed to do on their site. i think communication platforms should allow all (legal) posts
Do you? Really? Seems like everything would just be a spam-and-troll-filled wasteland...
There's nothing that prevents the President from being one of those trolls, and there's no strong reason for any given platform to give him special treatment forever if he persists in that behavior...
(Which is good, just like having a bouncer at a bar - punching someone in the face may be someone's genuine behavior, but it's not very welcome.)
You're very eager to weaken the private property rights of others, as well as to give a LOT of power to the government (legality as the only consideration) and I don't think these thing would work out for you like you hope.
Trump is still free to say whatever he likes, and Twitter is still free to moderate its platform.