A number of company's and organizations have long rewarded their clients and customers for particular choices or behaviors. Auto insurance companies will provide discounts to long term customers that maintain a clean driving record. If individuals can enjoy a discount for being a conscientious driver then surely they should receive a similar benefit for maintaining their health. The notion just makes sense as both the insurer and the insured will save money over the long term.
Yes, people who take positive steps toward health promotion and disease prevention should receive discounts on their health insurance, because they have lowered their risk. If someone is less likely to need to use their medical insurance because they live a healthy lifestyle, they should be rewarded by having a discount.
We do this for car insurance and it makes sense (no tickets, lower rate). I believe people that are being proactive in disease prevention and are actively maintaining their health should receive discounts. It will motivate others to do the same. Overall, this will lead to a healthier population. I think that is a good thing!
I do not believe it is proper to award people for taking care of themselves. Humans should feel compelled to watch their health and take steps to prevent disease naturally. I don't see any reason to offer discounts on health insurance for these reasons. It may make sense at first, but financially it is not a sustainable practice.