I think it's worth at least considering that we should give up on relevance. As far as I can tell, nobody has figured out a good way to decide what ads are actually relevant to an individual. So personalized ads tend to come come in one of two flavors:

  1. A blast of ads for something you just bought.
  2. A blast of ads for something you just decided not to buy.

At best, ads like this deliver zero value to both advertisers and consumers. At worst, they creep people the heck out. Which means they hurt consumers by making them feel stalked, hurt advertisers because nobody wants their brand associated with creepy stalker behavior, and hurt publishers because it only accelerates the proliferation of ad blockers.

This doesn't mean relevance needs to go out the window. People were targeting their ads well before it became vogue to collect people's toenail clippings and feed them into collaborative filtering models. For example, if you're a high end diamond store then you shouldn't need a bunch of whiz kids from San Francisco to tell you that your ad would be better-placed on The New Yorker's site than on The Village Voice.

I dispute that serving ads relevant to the content of the site is "giving up on relevance." If anything it's far more likely to be relevant. And it doesn't require tracking the user.

If I'm reading a site about auto maintenance, for example, what's more relevant? Ads for auto parts suppliers, or ads for cookware because that's what I last bought on Amazon?

Serving personalised ads in the EU means you will have to show a cookie warning. That for me is reason enough to focus on contextual ads. Not that I am showing cookie warnings right now, I'm counting the days till they revoke that stupid law.