First on the analog to smoking. McArdle makes the common claim that she was a heavy smoker and quit without great, great difficulty. People are different. Tobacco companies used to trot out old ladies who were in their late 90s and claimed the secret to longevity was drinking, smoking and cussing. I exaggerate a little. Attributing cause of death to cigarettes is murky business; heart disease is not like getting hit by a bus.
In addition to Berger's sharp observation...
On the one hand, she admits that many people just don't have any substantial volitional capacity when it comes to food. On the other hand, she objects to any government intrusion into the "autonomy" of these people. How does this make any sense? Why should we safeguard something that doesn't seem to exist?
I will add that our choices do not exist in a vacuum. Junk food advertising is ubiquitous, much of it aimed at children and young people in their formative years. Moreover, these advertisements do not appeal to our sense of reason, our rational side, but rather the beast within the person. We can follow in Sweden's footsteps and begin by banning advertising to children.
The most common argument for a junk food tax is that we the public are paying for your health-care, so it makes sense for us to tax/create a disincentive for unhealthy/costly activity. McArdle and other conservatives/libertarians counter this by saying the government should not be involved in health-care at all; two wrongs do not make a right. I watched this earlier today, so I might be mistaken on the exact context, but I recall McArdle basically viewing a tax as only a deterrent. Well, obviously we can also look at it as a citizen paying her dues, internalizing negative behavior (whether or not that tax revenue specifically goes to health care or not).