I don't think it would be that much of an asshole to sell the data so that a user starts to see ads for their local gym in their Facebook feed all of the sudden

I don't think it would be that much of an asshole to sell the data so that a user starts to see ads for their local gym in their Facebook feed all of the sudden. You'd be making the world a better place by encouraging the act of exercising. And the lower cost of healthcare. It's pretty much up to you now!