A class action suit would be ineffective. Facebook has oodles more lawyers and bank than any amount of indie content creators could muster over the long haul in which a legal process would occur. We’re talking years here. It would be an endurance contest which Facebook would handily win. Meanwhile, they’d still be monetizing copyright infringements.
The court of public opinion is the only place you could hope to win this battle. And you’d have to mobilize a massive effort someplace other than Facebook because any activity whatsoever on Facebook contributes to the value of Facebook.
All of their value comes from platform activity. So the only way to hit them where they would possibly take notice is to reduce Facebook activity in the aggregate. You’d need to get millions of Facebook users to stop using or severely reduce their use of the platform. And there’s no guarantee that would be successful.
It really is a David vs. Super-Ultra-Mega-Goliath-Zilla scenario.