Your example is really reaching far in order to prove some "nefarious" effect, as you put it. In order to make the case for some weird "ad-based discrimination" you've put yourself in the role of the ad-space owner AND the ad buyer which really doesn't make any sense. It's in the interest of ad buyers to show their ads on websites that relate to their product, plain and simple. I'd say that the initial assessment of you being a "confused user who isn't really sure how privacy works" is proving to be quite accurate.