I agree with Cosmos. Like some types of insurers being able to require the release of your personally paid genetic test results from 23AndMe or Ancestry, if they don't request it, they can find services to buy your data and use it.
Pardon my sour outlook on the world of technology, but I expect this type of big brother data-mining behavior will happen whether we approve of it or not, and whether it's legal or not. Once you post personal information to the web, it's awfully hard to get it back or control what happens to it. This is why I don't participate in social media outside of a linked-in profile.