Since FB has gone out of their way to weaponize "friendship", my suggestion to everyone who actually likes to have some standards in their life and don't like to be manipulated like that is simple. Just do it back to them. "Unfriend" (IRL) everyone you know who works at Facebook and tell them you will "friend" them back once they leave the company.
I would never friend someone again who dropped me because of my employer
For instance, if I had a friend whose job it was to design missiles that are used to bomb innocent people (Lockheed-Martin for instance) I would seriously reconsider my friendship with that person. Yes, it's "just their job" but choosing to have a job which requires having such warped ethics would make me reconsider whether I want to continue associating with them.
Nobody is forced to work at such companies. Yes, effectively all companies do things which we don't agree with on some level (unimaginably large amounts of tax avoidance being the most obvious example). But if a company's ethics are completely antithetical to your own, then I don't see how you could morally justify working for them.
(Obviously there are some understandable exceptions to the above -- the most obvious being that in the US employees are effectively blackmailed into working for their employer because they'll lose their heath insurance otherwise.)