I think you’re overstating the privacy protections afforded to people’s health care data. While there are some protections when it come to health care providers, there are scant protections when it comes to the employers themselves, who may very well be making health care decisions on behalf of their employees in terms of the kind of coverage they offer. Even more dangerous is the lack of protections against discrimination based on "unprotected’ behaviors such as physical activity, diet, or other activities outside of work, or even likelihood of developing a disability (i.e. diabetes, hypertension, pregnancy).
It’s also worth pointing out that while HIPAA prohibits discrimination or increased fees based on health status, when a company creates a discount program for people who are willing to part with their data, exercise and make changes to their health, they’re essentially creating a negative discrimination system, where those who don’t do those things pay more, both immediately because they don’t get a discount, and in the future because health care costs are shifted from those who track to those who don’t.
I think there’s legitimate concern over the use of fitness trackers and collection of personal data by employers, and that there are insufficient protections for employees. I don’t think it’s paranoid to be wary of how these devices and data are being used, especially in light of cases like Burwell vs Hobby Lobby, and the potential roll-back of consumer protections in the ACA and other legislation.