If they WFH, then nothing will prevent them from 'copying' any material they want, even if by cellphone photo of the computer screen, no?
But if you have privacy expectation on fb...
I dont think that would hurt anyone then
Why would anyone use FB for that? It is already very hard to run legal sex related groups on FB. Registration is pain etc..
Some other social networks are full of porn, but even those have zero tolerance for this.
So I think the privacy expectation for that kind of thing is low.