It would be easiest to just ban ads targeted by anything OTHER than the non-customized on page content. It's fine for ads to be targeted based on what's seen. It's _possibly_ OK to target ads by __large__ regional geographic area. (E.G. traceroute seems to say your IP is near Major Big City, so that huge region or a TTL circle around it is an OK ad pool.)
Anything more specific is ripe for abuse and should just not be allowed. Comparatively that specificity would be roughly equivalent to traditional TV, Cable and 'Print' media.
This is specificity as consumer privacy protection. I'm against most types of ads generally from a mental health stance.