I don't think that government bans or taxes on food products that they deem to be unhealthy is the way to fight the obesity epidemic in the US. Why stop at soda? Why not include french fies, salad dressing, beer, big macs, cheetos, processed food, sugary cereals - the list is endless. Should the government penalize people who don't exercise enough by having them pay a fine if their BMI is above a predetermined amount? That would interesting and impossible to implement.
If the government is going to get involved, I'd rather see the money diverted to education programs that encourage healthy eating and exercise - especially among the young. I do support the high taxes on cigarettes but I don't think this should be applied to food products to discourage consumption.
I do agree with you that people who have made unhealthy life-style choices should pay more for healthcare insurance although this is difficult to implement under a nationalized healthcare program. Some healthcare plans pay you an incentive amount to lose weight, stop smoking, etc. This might motivate some people to shape up but those who continue to engage in unhealthy choices should probably pay more one way or another. Of course, the ultimate payment these folks incur is shorter life-spans which is a heavy price to pay.