OK, so how much higher do you think it should be? And based on what?
What is the difference, in years, of the death age of people that are obese, overweight, or of "healthy" weight? I suspect that you'll find that there isn't that much difference between the two.
Another question; should obese people get away with paying less into social security since they are likely to die sooner and therefore collect less money?
I'm not trying to be a wise guy here; just trying to point out that there are some other issues at play.