I'm not from the US, so I have only got, at best, biased second-hand knowledge on your "obesity crisis", but I think in most countries, including my own, such a "junk food tax" law would mainly punish those people who can't afford daily home-cooked organic meals anyway. cynchick makes some good points about the cost of health food and the importance of work in most people's daily schedules -- you just grab a bite and stuff yourself with a sandwich during a 10-minute break. It happens to me on a regular basis, and I only work about 42.5 hours most weeks.

Moreover, it strikes me also as an excellent way to indulge in some obesity-panic moralizing that makes overweight people even more ashamed of their bodies than they already am. (Note: I'm clinically obese so I know what I'm talking about.)