I never had soda when I was in school, or vending machines. We had milk and juice. Of course one can argue about milk too, one can argue about pretty much everything. Obviously kids will drink it at home, at the mall, etc. But I see nothing wrong with schools trying to do their part.
I drink a Diet Pepsi (caffeine free, used to be caffeine) practically every day, I know I should stop. That's all though, when I'm out I usually have just water. Other than that I drink lower fat milk, water, and sometimes juice in the morning.
Soda can be very addictive, I have known many adults who become addicted to it. What about stuff like Red Bull? Kids drink that too. I'm always surprised when I see parents let their kids have Mountain Dew and the other highly caffeinated sodas, not to mention the sugar content.