Should overweight people have to pay more on the plane?

Why should people of normal weight pay to subsidize overweight people? Don't they also make the plane use more fuel which is bad for the environment? You have to pay for baggage of excess weight--why shouldn't you have to pay if you're overweight as well? Wouldn't it be an incentive for people to lose some weight too, and therefore good for public health in general? (I don't mean pregnant women by the way--they could carry a medical cert which would excuse them from being charged extra.) What do you think?