No need to go full denial. Insurance is priced according to risk. If I've got a record of accidents and traffic violations then my car insurance costs more. If I'm 100 lbs overweight and hypertensive then life insurance costs more. Medical insurance can be priced the same way, creating incentives to maintain a healthy weight and diet.
The problem with your theory is that driving is optional and not something we engage in 24/7. Being alive is a continuous thing and we don't understand all the myriad things that contribute to stuff like weight gain.
I was seriously overweight for a time. It did not get better until I was diagnosed with a genetic disorder and began getting proper treatment for that. Until I had a proper diagnosis, my body just did not seem to work the way everyone told me bodies worked.
I ate healthy. I exercised regularly. I was well educated and well read. Yet my problems seemed to defy solutions for a lot of years, until I finally got the right diagnosis.
Most people who are overweight wish they could solve it. They often don't know how, even after taking all the usual advice.
New research into things like gut biome is beginning to cast light on such phenomena, but this is hardly a solved problem, contrary to what many people seem to think.
Insurance is priced according to risk, yes. However, most insurance is priced against fairly good odds that they will not pay to an individual. Which ultimately points to health care being a relatively stupid place to trust to an insurance market.
I don't necessarily disagree, but I think you start getting into challenging grey area with pre-existing conditions. Is being overweight a consumer responsibility but an auto-immune disease isn't? How do you effectively draw a line between disease or health risks someone should be responsible for versus not.
Well ideally you have insurance before the "pre existing" condition exists (or is discovered).
However in general I think pre-existing conditions need to be handled by something other than "insurance" and the trick is to do it in a way that doesn't incentivize people from foregoing insurance until they get sick.
And since it costs nothing to post better, it seems fair.