That is a real problem. In a perfect world you would want all of your data to be available to everyone who can use it to improve your live. And only getting advertisement for things you actually want/need (not only think you want/need) is a real improvement of your live.
Sadly “improving lives of consumers” is not the goal of any of the big data collectors and as such any data collected is or will be missused to cause harm to the owner even if it is not directly obvious.
Google is the master of fake Privacy features - gHacks Tech News (www.ghacks.net)