My point is that it's mostly the poor who have these vices and who are overweight/obese. So, if we are going to charge them a surcharge, then we are actually charging ourselves a surcharge too, since we pay for their health insurance through taxes. Therefore, the proposal doesn't really make much sense and would only make health insurance more expensive for ALL of us in the long run.
Assumably the more pricy we make a product, the fewer people will purchase it. Italian sportscars are very expensive, so not many of us drive them. The more poor someone is, the more sensitive to prices they are, and thus the better the disincentive effect of higher prices.
If we had a higher tax on sugar and fat filled foods, then the fewer of those foods the poor would purchase, and thus there would naturally be fewer overweight people, or at least they wouldn't be as overweight. this would result in a lower national healthcare bill, and would thus result in lower insurance prices for all of us.
The side effect of increasing this sin tax would be to collect additional revenue from those who tend to be the worst abusers, this revenue could be used to subsidize the insurance risk of insuring fat people.
Basically the way I see it, we have few options. We can allow insurance to become so unaffordable for faties that they just don't purchase it, and then we can just let them die untreated.
Or we can jack up everyones insurance rate just a tad, essentially charging healthy people for the bill of avoidably unhealthy.
Or we can keep their insurance rates modist by subsidizing it with revenue from bad food choices that they make. This seems to be the most human and sensible option. This way most everyone can acquire insurance, but those who tend to create their own health care costs will pay for those costs at the cash register (a little at a time, in a manner that is perceived as being affordable, and in direct proportion to the amount of bad choices that they make), instead of externalizing them onto other people.
You have to step back and look at the big picture. I don't like to use the word "fair" in an economic discussion, but this is certainly practical.