It incentivizes companies to gobble up any and all data they can about people. It incentivizes companies to increase the silent intrusion into our lives. It incentivizes companies to forget their "markets" are actually people -- extracting value from markets is taking resources from people.
Hypothetical scenario - with 23andMe and other DNA profiling places being targets for lots of different kinds of data thieves, what are the chances that "leaked" datum ends up in some kind of ad profiling system? Ad companies might know you have cancer before you do because your genetics hint at it, your purchase history hints at it, your online behavior changes might hint at it. Yet instead of alerting you that you might have cancer, they use those hints to sell you "life extending supplements" or homeopathic remedies promising to fix one of the symptoms you have. They squeeze you for money while you are still alive to be squeezed because you aren't a person, you are an ad profile. A cash cow.
Ad companies are not out for our benefit, they are out for their own. Just like every other company whose goal is to make money, they will throw people/consumers under the bus to save profit. So why would we give them any more leverage over us?