This line bothers me because the relationship is more complex than that. You are receiving services from Facebook and in return you are giving them your information. Facebook does not sell your information to anyone - instead they sell the ability to advertise to different groups of users (who you are one of). To say that you are the product implies that companies are getting "you," but they are only getting ads displayed on Facebook. They do not have any idea about you or your specific information.
If you don't give Facebook information, it directly hurts Facebook. If you don't browse Facebook, it directly hurts Facebook. Their revenue absolutely depends on users enjoying their service.
Broadcast television uses a similar model, but no one accuses them of "selling" their users.
I'd take it a step further though and say the entire "you're being sold!!!eleven" isn't contingent on the level of information an advertiser gets about you (of which, like you said, they simply don't have), it's a pithy saying with zero basis in reality used by those with a hipster mindset, who feel somehow superior for not using that damn money grubbing Zuck's advertising site.
If you (the general you, not you you) don't want to use Facebook because it's a timesink, or because you don't have friends on it, or because it could cause you negative real life consequences, or whatever else fine - just do me a huge favor and spare me the breathless moralizing and predictions of dystopian "papers please" futures. You don't have to justify yourself to some random on the internet, and I kind of wish you wouldn't besides.
Yes, they're scummy. But they didn't force you to put your personal info or photos on there. Don't want the internet to know something? Don't post it on facebook.