... If somebody learns every detail of the motions I make when I brush my teeth...
While your comment sounds like over-the-top sarcasm, keep in mind the time when you go to the dentist and your dental insurance company refuses to pay their portion of the bill because you have not been brushing your teeth properly....
There are two sides to that. How would you like an option to buy dental insurance that is dramatically cheaper, but which you can only get if you allow your brushing habits to be monitored and corrected? I think there's value in allowing people who choose to manage their risks well to be able to benefit from the reduced costs. For such a policy it would be important that you find out that your brushing is substandard before you go to the dentist, though, not after. It shouldn't be a surprise.
We do need to draw a line that prevents preferential treatment based on characteristics which are not within the control of the individual, including past behaviors, but I see no problem and lots of advantages in enabling the use of pricing to encourage behavior that reduces costs.