The argument that "if you don't pay for the product, you are the product" does not work in the inverse. If you are paying, you might still be the product. See also: your ISP, Spotify, your bank, etc. It is impossible for the free market to regulate itself with so much money on the table.
I hate advertisements. I loathe them with every fibre of my being. I'll do almost anything to get rid of them. Multiple browser addons, a pi-hole, using a browser instead of an app, modem and router tweaks, whatever it takes.
But the data collection? I don't care at this point. It's absolutely everywhere and totally unavoidable, short of living off-grid in the middle of nowhere. It's in the software, the hardware, the services, the organizations. You cannot escape it.
Yes, it sucks. But it's just part of living in a modern digital society now. It could be better but you can't avoid it.
Hell, I use an app on my phone to track my driving so I get an insurance discount. It's one drop in an entire ocean of data collection that I can't see or hear or taste, but the money saved is very real in my pocket.
How would facebook monetize non-ad-enabled customers?
Facebook doesn't sell data to other ad companies because that'd be giving away the very thing that makes it the most valuable advertising company in the world. Hell, we spend a huge amount on facebook, and it's impossible for us to get reports on basic things like "Spend per placement per hour".
The only area that I could see them _maybe_ still monetizing an opt'ed out user is with Meta Audience Network, but I bet they would still opt them out of seeing ads on 3rd party sites that have MAN ads in their stack because that business segment is likely small compared to potential PR and fines in the EU.
I guess I'm saying even if they aren't targeting an individual with that individuals data, they can use it to target other individuals who do see the ads.
Related to this, I seem to remember that there were talks about some start-ups doing this kind of stuff on millions of people’s profiles, this was before Cambridge Analytica, I wonder what happened to them. A former colleague of mine (very smart guy) ended up working for one those start-ups back in the day (2013-2014), that’s how I first learned about their existence and about their business model.