I suppose you could monitor people for what they do that adds to the price of your insurance, as long as they can monitor you for how fast you drive, what foods you eat, what your sleeping habits are, and anything else you might do that would affect how much they pay for insurance.
I don't understand your point. There are laws against driving too fast, and when you get nailed, your insurance goes up (believe me on this one). You may not get charged more for eating particular foods, but you most certainly do for smoking and for certain recreational activities.
If insurance companies were allowed to do a real actuarial analysis and charge more for high-risk behavior; or simply to exclude AIDS from coverage, I'd have no problem.
As it is, as long as the taxpayer or the insurance companies pay to treat brain injuries, I support helmet laws. And as long as we pay to treat diseases caused by massive promiscuity, we have a right to pass laws regulating sexual behavior.