Obvious lie. The current government is controlled by the group pushing the "stop the steal" propaganda. No reasonable person would believe Trump's own government is compelling Facebook to remove it.
> Can you imagine the shitshow if they banned, let's say, black people?
Sure... And what, pray tell, does that have to do with removing _posts_ containing calls to violence? How are those two things comparable?
Nevertheless, I'll indulge you: While businesses in the USA generally reserve the right to refuse to do business with whomever they please, Federal law (under the Civil Rights Act of 1964) prohibits discrimination in public businesses made on the basis of race, color, religion, or national origin. Many states also have their own laws further limiting discrimination, though I'm not personally that aware of how these have been tested in regard to online services serving many states/countries.
Beyond what's required under law, companies can have whatever policies they wish (but will have to deal with public outrage for implementing policies as disgusting as the one given in your example).
Because there's a clear government-enforced bias. Can you imagine the shitshow if they banned, let's say, black people?