During COVID, there were people spreading lies about the vaccine, which many people believed, and many people died as a result of believing those lies. Even Louis Brandeis, one of the fiercest advocates of free speech, made an exception for emergency situations[0], which is arguably what a pandemic is.
But again, lies about a vaccine do not constitute reasonable public discourse, it is more akin to screaming fire in a crowded theater. If you have counter examples of regular public discourse that has been censored by a social media company, please share it.
* I realize "ever" is a stretch, I'm sure there are instances, but my understanding is that they are the exception rather than the rule.
[0] "If there be time to expose through discussion the falsehood and fallacies, to avert the evil by the processes of education, the remedy to be applied is more speech, not enforced silence. Only an emergency can justify repression. Such must be the rule if authority is to be reconciled with freedom." - Louis Brandeis, Whitney vs. California