I can easily imagine a reality where insurance companies have access (intentionally or accidentally) and give you a higher premium because they found something that makes you more predisposed to some ailment.
The above is pure speculation, but it's only one security breach or bag of money away. It's never safe to assume that a your data is 100% secure at a (presumably) benign company. As curious as I am regarding certain aspects of my heritage, the fact that I have no control over what they do with the info is keeping me on the bench.