It already exists. Lots of employers use health screenings and offer reduced premiums if you pass them. Mine has one but it is pretty easy to pass, you can fail 2/5 criteria and still get the full $700 credit. So you can fail BMI and waistline and still get the full premium. If you fail 3/5, you get a $350 credit. You can fail them all and still get some credit just for doing the screen.

All other forms of insurance are billed on risk. That there's a social sensitivity toward categorizing obesity as high risk is just silly; obesity is incredibly high risk and it's reasonable for the insurance company to bill it higher. It's important to point out that this is obesity, not merely being overweight or out of shape. I don't see a ethical dilemma about insurance being more costly for someone at a 30 BMI.

With that said, obesity really isn't a MAJOR health risk until later in life. There's not a high risk of death in the current calendar year for an obese 30 year old so the usual year-to-year employer plans don't put a lot of emphasis on it. The complications from it explode once you cross into the late 40s, 50s and 60s, though.

The point of contention seems to be that some think obesity should fall under the same category as something like a tobacco surcharge and others seem to think it should be treated as something like Type 2 diabetes, a pre-existing condition more or less beyond your control.

It's probably somewhere in between.