Let's take a concrete example: how about people swapping recipes for chemical weapons and discussing their efficient deployment against unknowing civilians? Or people discussing and developing (largely anonymously) the logistics of mass shootings, with a view to maximizing the body count?
They're just having a chat. It's unethical to censor them. Perhaps they should be brought in on some other charges, but there's nothing illegal about talking. They're not threatening to kill anyone, are they?
In practice, you see this as well. There's a lot of people posting on the Internet about how they're going to do this and that, but in practice most of them are just blowing off steam.
I get why a site like Facebook which wants to have community standards would like to enforce it, but it should be up to the proprietor.
