The pie-in-the-sky fantasy land of future low interest credit card leads [which is the exact opposite of the sort of offers such a site would get. The best would be predatory, secured credit-card type offers] and automatic...something...it just has the aroma of failure. It could as easily be a "lose weight today" website where you enter your desired weight and it tells you to eat less daily. Which...if such a site existed...I think we would all laugh at.
They'll have to make it super easy to use though.
As an aside, while this demographic has less total buying power than that of responsible consumers, it's also a hell of a lot more likely to buy stuff. Possible net positive?
As for weight loss, there pretty much are sites like that. fitday.com, livestrong.com, etc. None of them are magic pills, just like ready for zero won't be. All sites like this require a user who is determined and willing to make the change. But these sites can help the person who really is looking to make that change and increase their chance at success.
I think its popularity indicates a good opportunity.