Point one:
BMI is not the best way to measure obesity. I have had a BMI close to 30 without having much fat. Think of all the muscle hunks that falls wrongly into this statistic. I know that the strong men that compete in Viking games or Worlds strongest man have BMIs reaching the upper 40ties and a few that crosses the 50 mark.

Point two:
Fast food should be more expensive. The cheaper option should always be home made.
A whooper meal should cost around $20 and a large pizza at pizza hut should cost around $50.

I think people that really is obese, have a problem. Their addiction is food, and you can't just take it away as they will get sick.