I'm not sure if it's appropriate in this case, but I'm far more in favour of sin taxes than outright bans.
Like I said, I don't know if I'm in favour of that in this case.
On the one hand, it is clearly a harm that a person is doing to themselves if it is even a harm at all. (On the latter: there are days when someone may drink excessive amounts of sugar water, even though their nutrition is good over all. Do we really want to place restrictions on that?)
On the other hand, poor nutrition is a huge social problem that industry contributes to. Even if you ignore their attempts to persuade people to make unhealthy choices through advertising (and yes, the bulk of advertising seems to be geared towards unhealthy choices), you also have to consider product availability. Consider the bulk of grocery stores. While they do offer plenty of healthy choices, the bulk of the floor is dedicated to prepared foods (including drinks) that are chock full of sugars. Consider eating out. Many places offer nothing beyond sugar water and coffee. Even the things that pretend to be juice aren't terribly different from soda, outside of the lack of carbonation. When they do offer proper juice, it typically has sugar added -- though certainly not to the degree that non-juices have. So if you don't have a healthy choice, people are usually going to make an unhealthy choice.