I'm convinced that discussing ethics or politics inside Facebook or Twitter will have literally zero effect. Employees should either quit or get back to work.
Why are you convinced of that? Unionized protests frequently accomplish institutional change - why do you think Facebook or Twitter would be exempt? If anything a unionized tech force striking would have more bargaining power than other groups since they are educated, specialized, and difficult/expensive for either company to replace en masse.
I agree that unions could be effective, but I also doubt that Facebook/Twitter employees could ever unionize. And for anything less than a full strike, leadership will just ride it out.