I could say that you'll be even fatter if you substitute whole milk for Coke, ounce for ounce, because you will be.
I could say that the extra nutrients in milk don't do anything to make it less fattening, because they don't.
I could say that 12 ounces of soy milk has 198 calories, which is still well above Coke's 140.
I could even say that switching to skim milk doesn't help you all that much — if you do the math, you'll find that there are 124.5 calories in 12oz of skim milk, compared, again, to 140 for Coke.
I could also point out that a tall Starbucks Frappuccino — also 12 ounces, and not covered by the ban — has 190 calories, largely from sugar and fat.
I could ask: Does anyone ever order a plain Frappuccino? A tall mocha Frappuccino has 220 calories.
Finally, I could point out that banning vending-machine drinks while leaving Starbucks untouched is a pretty rank example of class privilege at work — my indulgences are sophisticated and upper-class, while yours are vulgar and prole.