The problem isn't that data is being harvested when they use Facebook, it's also that data is being harvested behind their back with FB stalking everything they do online (since the majority of websites and apps include FB malware) and linking it back to their user profile.
Clearly most people aren't aware of that (nor are they happy with it) given that some people even have the impression that Facebook is literally listening to conversations.
For me it's not that I don't care, but I reason the data stealing as their form of payment for providing a free useful service to me. I try to limit the data I give them, but I still see the data gathering as their win in our nonzero (win win) game.
> but I reason the data stealing as their form of payment for providing a free useful service to me
In this case, they could very well be transparent about it, and comply with local laws/regulations (such as the GDPR).
When companies comply (or Apple forces them to - like with App Tracking Transparency), it's clear that the majority of people do not consider this a fair deal and opt-out.
As for me, I would use an alternative platform in a heartbeat, but all the privacy focused ones so far have not gained any traction.