I'm not for weakening privacy, but I don't see what's wrong with unhealthy people paying more for their healthcare and healthy people paying less.
On the surface, many of us would agree with that.
However, two (of likely many) issues come to mind (regardless of the privacy issues).
1) What is "unhealthy", exactly, and who gets to define that? How reliable are the measurements from the apple watch? In a parallel example: How will it be used? Formally, until the late 1990's, where I live here in North America, being gay was a mental disease, and technically I could be turned in to mental hospital for aversion therapy and lobotomy if the aversion therapy was not successful. That’s very recent still... Who sets those rules? If you are outside the norm—or their definition of healthy—in any way, what happens? From my perspective of being in medical research, this is an ugly area where money perspectives could wreck havoc (did you spend more than 20 minutes at your computer without a stretch and eye-break? You could be at risk for: hypertension, heart attack, stroke, diabetes, obesity, constipation; there is a correlation with increased stress, which could also lead to...etc.) Not saying forced 20 minute breaks are bad, but will all employers ensure this as a right? Can all employers afford, or work into all environments, standing desks? How the concept of healthy/unhealthy gets implemented will be to the insurance companies' benefit, not the individual.
2) Many people will fall through the cracks, in a bad way. My husband slipped on a friend's stairs, it caused at tiny hernia that required surgery. It seemed fine for 6 years, then we went through a period of 17 years and 9 surgeries to repair the damage from the deep, infected stitches. Due to time limits we could not sue, and physiotherapy/rehab therapy was at our expense, and much needed because at times it was even painful to walk. He also over-ate because of depression from the pain and being bed-ridden at times; he used to be an active runner, hiker, and volleyball player. He's still overweight and struggles with joint pain, and ongoing pain from all the scar tissue from the repeated surgeries. Now, our doctors just tell him to "loose weight" and "be more active", which continues to be difficult. He watches his diet carefully, but it's an ongoing battle, with no support, and he lost his job/had to retrain, again at our expense. Because of our problems, we know of many others in situations like this. One incident, not your fault, can change your life forever. The insurance companies don't care.
So, would I want my insurance company monitoring my every movement? Every change in my heart rate or my blood pressure (and whatever new iterations of the watch may bring)? No. In a field driven by profit over care of the individual, we'll all start losing out on money-driven decisions, offering our own data to disqualify ourselves, even if *we* think we are "healthy".