It is a more complex problem than this. What about when we find genes that predispose certain people to higher rates of cancer or other high mortality diseases? Obviously obesity is a problem. Most obese people have a much more significant amount of healthy problems than those who are in a decent weight range. It isn't just taking time off or being sick -- it is the health care costs that they cause by having more diseases, more illnesses, and a higher rate of serious problems.
There's going to be a slippery slope here. Smokers already face higher premium -- some former addicts and alcohol abusers do as well. Eventually the healthcare system is going to buckle because not everyone is predisposed to the same level of healthiness. Some people are a lot more unhealthy than others -- even if they are not fat or never smoked. Somehow that risk has to spread around. Either you can raise premiums for all or you can raise premiums for those who are at a higher risk.
Additionally, we cannot forget that we are extending people's life cycles beyond what the human body was once capable of. Until evolution plays a role (which is highly unlikely to happen in our lifetime), healthcare costs are going to rise for all of us. Not just the elderly that live past their body's ideal age, but also the younger who no longer succumb to diseases that killed off the weak in the past. Congenital defects and other problems can now be treated with surgery, and other syndromes and diseases that once caused deaths as an infant or teenager are now being effectively treated -- but to the extent that they just prolong life by a decade or two.
What about the amount of people who are alive now due to vaccination programs and better preventative health care? We've got millions of people walking around that would have never lived had health care not advanced. By the same token, we've got millions of weaker people walking around, because they survived due to vaccinations and advanced medical care. This isn't even counting the much higher survival rate of those with cancer, severe trauma, or other maladies.
Let's face it -- rising health costs are not just a factor of malpratice suits, crappy doctors, overbilling and graft, fat people, smokers, or any one cause. It is a multitude of causes, and there's no system out there that is going to be a 100% fix. All we can do is ride it out while healthcare advances even more.