No matter what the written policy says, they will have to tolerate threats of violence done in the name of political correctness. I remember the huge Twitter outrage from the well-connected social justice activists in the tech community driving policies like this when Twitter banned someone for threatening violence against a celebrity in the name of social justice, the anger that Twitter didn't understand this was important activism, forcing them to back down. It's politically impossible to act otherwise. Even Twitter probably only broke the unspoken rule by accident - a bunch of conservatives subsequently sent the same person threats, and most likely someone didn't bother checking everyone's political affiliation before banning.