* They don't care about the money and don't want ads on the site.
* They're someone whose content is the advertising. A database consultant might write an article on using indices to speed up low-selectivity queries. He doesn't need to plaster his site with ads, but his articles do serve a secondary purpose of advertising himself. Or something like Angie's List, where people literally visit the site with the goal of being advertised to.
* They don't mind unintrusive ads, and these help provide money and motivation to work more on the site. Google ads would be acceptable here.
* In addition to their site's primary content, they also write sponsored content for companies that give them enough money.
* They only care about extracting as much value from their site as possible. They might hire ghostwriters on Fiverr to write cheap articles, apply SEO techniques to get them to rank higher than they should, and then plaster noisy ads and popups everywhere. They might buy cheap traffic on low-contested keywords, and redirect them to sites with more expensive ads to arbitrage the traffic. They might have a form to collect your name, email address, and phone number; and then sell your information to a mortgage reselling company. They might have loud ads that play music on page load, that automatically play video, that pretend to be a Windows error dialog, that look like download buttons, etc. Some of these are arguably the ad networks' fault, but the maintainer of the website is ultimately responsible for anything that appears on his website. They might release news articles with clickbaity headlines just to drive traffic to their ads.
I think most people take offense to #5. A minority also take offense to #3, since these track location and can form profiles of you between pages. I don't think anybody really minds the #2 or #1 people.
If you banned ads entirely, you'd still be able to monetize using method #2.
This is where I think tracking went wrong. Advertisers were so happy they could track users that they (kind of) forgot to track the content. I think basing ads on the page content is, in the end way more safe and beneficial to everybody.