Society is an abstraction for the aggregated product of individual actions. It's an abstraction layer above the level of individual choice, much as thermodynamics is an abstraction layer above mechanics.
Now lets suppose we do want to work on the societal abstraction level. The problem is that the proportion of people making a certain individual choice has gone up. One solution is a pigouvian tax to disincentivize this choice.
I agree you can't blame every single obese person for eating too much. You can only blame the vast majority of them - a small fraction really do have thyroid issues (and could potentially be excused from said tax).
1) people want line item veto from taxes? Where can individuals opt out of paying for wars they don't agree with?
2) taxing obese people would (beyond all the moral and ethical questions that arise) disproportionately affect people that already screwed by the status quo, people of lower income that cannot afford to eat better.
Obesity is a symptom, in the same way that homelessness is a symptom of a failed policy towards mental disorders. Just as some people treat depression and PTSD though alcoholism, some people consume unhealthy food that is cheap and keeps them going. The same reason that demographic also disproportionately smokes, it's a cheap chemical hit that keeps them awake while working two jobs.
...people of lower income that cannot afford to eat better.
People of lower income can't afford to spend less money on food?
...keeps them awake while working two jobs.
Please familiarize yourself with even the basic statistics on poverty in the west before discussing this topic further (hint: google the fraction of poor people who work).
You can achieve this tax without hurting those who don't overeat and under exercise, the same way we tax smokers and drinkers without hurting those who don't do either; tax it at the source, the food itself. Set up a tax system on junk food, etc. or something similar.
Now lets suppose we do want to work on the societal abstraction level. The problem is that the proportion of people making a certain individual choice has gone up. One solution is a pigouvian tax to disincentivize this choice.
I agree you can't blame every single obese person for eating too much. You can only blame the vast majority of them - a small fraction really do have thyroid issues (and could potentially be excused from said tax).