I also wonder if such a tax was levied, if soda companies would just swallow the cost of the tax. Soda is notoriously cheap to make (thanks to subsidized corn among other things), and that's why it is often one of the things comped on a menu or given free refills. The most expensive thing about a can of coke is the can. Perhaps such a tax wouldn't act as a deterrent at all, since it's very feasible that the companies could eat the cost of the tax and still pull a tidy profit.