Now if you have been looking for something else that you want to keep private (gay clubs, abortion clinics, or anything embarrassing) then your phone has betrayed you.
There is also a point that if the ad is more useless, the quantity of ads should decrease because advertiser will not find them worth it.
The problem with accepting being under constant surveillance to make advertisers money is that the data is never just used for ads and even if you never show your phone to another living soul that data never goes away and can end up in the hands of just about anybody.