The nuance in the US is that this is censorship by corporation, not by government, so extant laws against censorship (which are aimed at the government) don't apply.
I think it's past time that corporations for social media of a certain "size" be recognized as public fora, and a body of law be developed regarding their behavior and responsibilities. Facebook, Google, etc, should not be censoring. Where this gets tricky is that both the corporation and the internet tends to span borders, so jurisdiction becomes very complex. Someone in country A uses a service in country B to interact with someone in country C. Which country's laws apply?
That is the problem. In the absence of legitimate power, illegitimate power is operative, and today that is Facebook and Twitter; they are serving de facto as quasi-governmental entities regulating interactions between citizens, since real governments have been unable to do so.