I agree that we should end the crop subsidies (Beef, too, but that's a different issue). I also agree that we should allow the healthcare system to charge extra for an unhealthy lifestyle. However, both of these things would help the problem in the exact same way as a sugar tax: by making sugar more expensive. How do these things not disproportionately affect the poor, but a sugar tax does? They have the same effect on the consumer!

Sugary drinks are popular because 1. they are cheap, and 2. they are addictive. What would change this is making sugar more expensive. I am unconvinced that the health consequences of consuming so many high fructose drinks are not an externality. I think it totally is, the exact same way that lung cancer is a negative externality of cigarettes. Less people smoke now in part because of a culture shift, but also in large part because cigarettes are more expensive now. Obesity, and other metabolic syndrome symptoms, is not just an American problem. Obesity is now an epidemic in nearly every wealthy country.