You can buy two meals if you like. The policy applies a cost disincentive to unhealthy eating, an approach which has proven success as a disincentive for nicotine addiction and alcohol consumption. Since society pays a steep price for the pandemic level of obesity it is justified to apply a modest price signal. And while the effect on each individual is small, the benefit for some individuals is enormous -- they will avoid the effects of obesity, like type II diabetes, and live longer lives. Your tiny soda sacrifice will save lives.
In contrast, obesity penalties at the level of some insurance companies is really extreme, to the extent of controlling their daily actions, and leading them to seriously consider use of dangerous weight loss drugs (amphetamines basically) and major gastric surgery.
There is no need to construct an enormous and improbable straw man if you want 'nanny state' regulations, there are plenty of examples. For example, alcohol sales policy. Why can you buy lite beer in many places in the US, but not full strength beer or wine or spirits? It isn't because of cheap drunks -- they are cheap and buying in bulk, a $40 bottle of wine isn't going to interest them. It is a hodge podge of local and state govt regulation with little tangible benefit.
The difference between good and bad regulations is often whether they are based on evidence and statistical re-evaluation, or knee-jerk politics. Well considered policy will identify groups that suffer detriment. I can't identify a group that will be harmed by discouraging discounted soda.