Yes, America has a weight problem. Yes, Americans drink too many sugary drinks. We also eat too many sugary foods, and suck down empty calories in other ways. Why is that? It's largely (no pun intended) because we have a tremendous surplus of extremely cheap, empty, non-nutritional calories in our food supply. And why is that? The Farm Bill. We subsidize corn to the tune of billions of dollars per year, and we grow way more of it than we need. That corn gets refined into high-fructose corn syrup, which is then poured into food in obscene quantities.
Subsidizing production then taxing consumption is insane. We should stop subsidizing the production of this crap and let prices rise to more natural levels. This wouldn't be great for Coke, Pepsi, McDonalds, Starbucks, Hostess, or any of the other companies that stuff our food with this crap, but I'm OK with that. In fact, I'm more than OK-- I would be ecstatic.
Alternately, we could put a hefty tax on refined corn. I understand the value of creating incentives to ensure an adequate food supply, but if it's gotten refined into sugar then it's clearly above and beyond the amount that we need in order to feed the country.