If they are going to charge more based on bmi they out to at least do it scientifically. Overweight have better overall mortality numbers than normal weight. What about underweight.
It's no more prejudice than charging a guy with 10 speeding tickets and a Hemi more than the lady with no tickets and a compact car for car insurance.
I am 37 years old, and have a 27.5 BMI. Do I get penalized? I am running at 12-14% body fat, you can see my top two abs, and I just ran a 23:03 minute 5k.