Class action just means there are numerous plaintiffs being represented.
What I’m saying is that the process for this kind of lawsuit would take years. Lawyers cost money. The average lawyer makes ~$150/hour in my part of the world. That’s around $300K/year just for 1 lawyer. A lawsuit like this would need more than 1 scrappy lawyer. So add to that any other lawyers, court costs, research fees, evidence collection, etc. This could easily get into the millions of dollars in legal costs. Add to that any emotional duress from being in a lawsuit for years on end with no guarantee of success.
All Facebook’s legal team would need to do is stretch out the process as long as possible to make the plaintiffs’ legal costs insurmountable. No money = no lawyers = no lawsuit.
And during that time, they’d still be allowing copyright infringements to occur and be making revenue from freebooted content.
This is why I say the court of public opinion is likely to provide a more desirable result. Especially because the public and the expression of their opinions are Facebook’s primary commodity.