Why not? Bad drivers have to pay more for car insurance because they are higher risk for accidents and hence claims, and smokers have to pay increasingly hefty taxes for their unhealthy habit. Similarly, fat folk are at higher risk for disease and hence more likely to make claims. Therefore it’s only right they bear a larger share of the burden. That’s not unthinking bias; it’s common sense. After all, why should everyone’s premiums be higher when not everyone shoves down donuts and fried chicken? Unlike some other health problems (such as types of cancer, rheumatoid arthritis, mental disorders, etc) we all have the ability to let ourselves go and get fat. Yet, some of us don't. Why should they have to pay extra for other people's recklessness?