Obesity is a huge public health problem, one the free market obviously has no incentive to solve, and thus requires public and government action.
Bloomberg’s idea is terrible. I can think of plenty of workarounds. “Buy one, get one free (or half off or whatever)” for starters. Selling large soda cups with “diet only” printed on them, but not making any effort to police customers filling their own soda drinks. Those are just two mediocre ideas off the top of my head.
Obesity for the most part isn’t a supply problem, it’s a demand problem. There are ways to Nudge the public into making better choices, but this sort of heavy handed ban just never works. Reminds me of San Fran’s ban on free toys with happy meals. The easy work around? Sell the toys for a penny.