I have absolutely zero problems with the concept of legit and reasonable ads. I fully understand and support why advertiser-supported content is a thing if I'm not paying anything for it. I guess can understand why some people that are holding on to this futile concept of "privacy" have a problem with ad tracking, but they need to accept (if not like) the fact that in today's online world, there's virtually no expectation of privacy for things like this. The internet is essentially a public place, and there is no reasonable expectation of privacy in any public place. So if a marketer wanted to hang out in a public market and write down what flavors of ice cream I like to buy so they can then hand me a flyer for their ice cream, meh, so be it.
Here's what I have a problem with:
* Intrusive ads. Ads that pop-up, over, under, and modal ads that interfere with my ability to access the content I'm after. It's bad enough on a desktop browser but browser extensions and other software can help control it. On a mobile browser where you have fewer if any options, it's especially infuriating where I'm scrolling for minutes reading a long article then the ad refresh timer expires and it reloads the whole page -- from the top. I spend so much time scrolling to where I left off, that the timer is close to expiring again and the process repeats itself. Ads that keep to themselves in a fixed banner, sidebar, or otherwise constrained area that I can ignore if I choose to, I'm fine with. And I'd rather see ads that interest me than totally random and uninteresting ads.
* Deceptive ads, not only the obviously scammy/malware ads, but the ads that appear to offer a legit download button for the content you're trying to access, only to discover it's a cleverly disguised ad button that takes you off the page to some shady service/product. That's the opposite of "legit and reasonable."
* Unskippable or dismissible ads, like video ads, that require me to wait through the entire presentation (or several seconds of it) before I can get on to my business. ESPECIALLY if I'm already paying something for the content (I'm looking at you, movie theaters -- though I realize it's not entirely greed driven since margins for cinemas can be incredibly thin).
If the ad agencies and related companies would better police their ads and enforce some standards, ads wouldn't bother me at all. Even better, offer a paid option to bypass ads, like YouTube Premium, which I happily pay for given the time I spend on YT and how disruptive forced video ads can be.