Instead of taxing soda, why don't we consider getting rid of the government subsidy for corn growers? If we did that, and corn (and the HFCS made from it) actually cost in the marketplace what it costs to grow and produce, and it had to compete in the market fairly alongside other choices, that "cheap" bottle of soda wouldn't be so inexpensive anymore. Nor would any number of products made with HFCS.
Another issue: The United States obesity epidemic began at the same time of the introduction of the current Food Pyramid. Coincidence? I think not.
A low-fat, high-carb diet doesn't seem to work for the majority of people, based on the results witnessed across a large population.
cheers,
Ian