Facebook and Twitter not being allowed to ban the sitting President would be a major First Amendment violation, in fact.

In certain contexts, harmful lies can be fraud, defamation, or perjury. It's reasonable for a social media company to have a policy that harmful lies are bad for their site, while still otherwise supporting free speech.

Trump claiming the election was stolen, vaccine disinfo - these are lies, and they're very destructive.

Meanwhile, the takedowns that are happening today are people being punished for stating the truth.