This is exactly the tension, the dynamic, at play, and food/obesity is not alone in having this public health vs. personal responsibility yin-yang. Think alcohol and opiates abuse as another.
Alcohol can be consumed without abuse and with real benefits, in moderation. Opiates can and are powerful medical tools when used correctly as part of treating serious pain. To no small degree abuse of both involves the abuser making a choice to do so. There is and should be some personal responsibility regarding how both are used.
Nevertheless as a society we recognize that society has an obligation to protect those prone to abuse from their harms. We in particular try to protect children from having unfettered access and from being targeted by those who would push these products. We also hold those who sell the products liable to some degree - a bar is liable if they serve too much and the intoxicated person then goes out and kills someone in a car crash; legal sale of opiates is restricts and tightly controlled and those who sell outside of those restrictions are subject to punishment.
There is a conflict between the threads of the responsibility for harm is on the one who “chooses” to consume, and the responsibility of “the state” to control those who promote the substances to those at risk or underage for profit.
We have a fair sense of that balance for alcohol and opiates even though of course abuse still occurs, especially as when the state fails to exercise its responsibility well. For the products produced by The Food Industrial Complex - substances, as described above, designed to be “hyperpalatable”, designed to be over-consumed, to hit the brain centers that say eat more and to bypass the brain centers that say enough, we have less sense of the balance. We are heavy on the personal responsibility side and we even include our youngest as among those for whom little protection from these abusable products seems to be required.
I do not pretend to know exactly where or how the balance should be hit. It is more difficult than for alcohol where it is fairly simple to pick an age to say none legally allowed before with only few exceptions. We’d all like to allow a treat here and there. Nevertheless the obligation to find that balance, to find a way that protects children from so much of the hyperpalatable that it becomes a health risk, to create an environment that does not overly encourage obesity in anyone biologically prone, exists. As does personal responsibility at the same time.
Meanwhile I can stretch this analogy even further. Best not to be a heroin addict in the first place but given an addict we want to reduce the harm. Minimally clean needles and hopefully to oral methadone and off the street drugs completely. Is being on oral methadone as good as being completely clean? No of course not. But the harms of being on methadone for a few years or even as long term maintenance are much less than the harms of abusing street drugs. Now in comparison the harms of being obese but down 5 to 10% from where you were and simultaneously having moved into the middle tertile for cardiorespiratory fitness are even more of a harms reduction.
Prevention is the first priority (by way of fostering healthy behaviors for ALL from early ages on, including by ways of controlling the food and exercise environment) but after that harms reduction is the order of business.