It is hard to understand the breadth of scope of the FAANGs. You read in the newspaper that Google exists to turn over dissidents to the Chinese government, but there are plenty of engineers working on making the Linux kernel more secure, or providing gigabit internet for $79/month. Should those engineers quit and go work on CRUD apps for some startup at half their salary? It doesn't make much sense, and that's why people don't do it.
(I don't know if the scope of Facebook is similar to that of Google, but I imagine it is. I submitted a patch to some open source project of theirs that collects diagnostic information from NTP servers. Are those people really to blame for targeting their product at 6 year olds? No. They just want to work on interesting projects for a great salary, and hope that whatever bigger system they're part of works out.)
Basically, it won't be effective to be an Internet Tough Guy and tell all Facebook employees to quit. They won't do it. Make their work illegal (regulate), or make their work unprofitable (stop buying their ads), and the problem solves itself.