Though... For the most part, we *do* know of the cost of religion. There's a pretty reliable financial (tithing and such) and social (both individually in the sense of being Christian in Iraq at the moment, fer ex, and also when we do things like outlaw abortion and gay marriage, or believe in the rapture and so don't care about the future generations, etc [when we should not believe in the rapture and still not care about future generations instead!]) cost related to believing in and participating in a religion.
So it'd be more like taking a weight-loss pill that you KNOW gives you (100% curable, not even a scar, but costs you a pretty penny) butt cancer, slightly imbalances your viewpoint (or not so slightly if you have a bad reaction and go all rain-man or something, i.e. fundies) and puts your life in danger in areas where overweight people are seen as the prophets of God, and therefore you'd be committing heresy. (or something, help me out here)
And that's assuming the pill even works, people who've taken it tend to go on vacation to Europe (or other place, if you live in Europe) and don't come back, leaving before the pill takes effect. Some people claim to be able to talk to them, but they won't let you do it yourself, you have to go through them. They can't take any pictures, but the medium of communication assures you that they've lost all this weight and it was all worth it.