alt Hacker NewsYou seem to be attacking a different statement that no one says: "if the product isn't free, you aren't the product". There's no "if and only if" in the maxim.
Pretty sure you agree that if the product is free, the company is definitely getting value by monetizing something else of yours. It very much is true as written.
From a formal logic standpoint, you're correct.
But the context of the parent's and grandparent's comments was (paraphrased) "if you don't pay, you're the product, therefore it makes sense to pay in this case". But given what we know of Meta and their ilk, we have good reason to believe this is absolutely NOT the case: you'll pay but you'll still be the product, and their offerings will keep on the road to enshitification. So parent comment is correct given this context.
I don't believe they were making the case that free Facebook is in any way healthy or good for you.