Targeted ads are the only way that small, new, local, or just poor companies can do advertising.
It's a bit scary seeing what sites show facebook you've been to: https://www.facebook.com/off_facebook_activity/ But if this is the price to pay to see quality ads within FB then so be it.
What I think is wrong, is then for facebook (or other apps) to sell, or leak that data in enough detail to match to our identity where it can be used for other purposes.