I have to say, I don't think government should have a say on soda size. Though I never drink soda, I'm certain that if a ban went into effect, I'd buy three sodas and march in front of the mayor's office just for spite.
On the other hand, if soda is making people obese and costing the city money, then perhaps there is an argument for banning things that are bad for people.
In a perfect world, people would be smart enough to do what was good for them. I'm sort of on the fence.
Michelle Obama answered the question like a politician: