That one's ability to easily become obese through junk food consumption is seen to, at least partially, define how "free" one is is pretty emblematic of what's wrong with libertarianism in my opinion.
Obesity can easily be fought by promoting healthier foods and voluntary means of eating wisely. Even a tax increase is more acceptable than this, in my opinion. We ban enough substances in this country and adding one more to the list won't make life better for people, whether it's healthy for them or not.
