If push comes to shove Google can do any number of things to fight against ads. For example, it started, silently, without explaining,for some who remove ads in youtube, to stop the video in the middle.
Heck even creating a credible enough rumor that blocking google search ads seriously degrades results could have a material impact.
This would be a good thing in the long run. It would open the door to paid services that could be competitive. Currently YouTube is free and there are no consequences for blocking ads. It's funny, I didn't even realize that YouTube had ads until I turned off my ad blocker one day. I was amazed at how awful the experience was...
In my case, I guess 90% of searches either include the term "stack overflow" or "Wikipedia", or get augmented by them when an initial search doesn't give desired results. I can't see how such searches might produce adverts that would help answer my questions.
It's very rare that I search for a product and even then, chances are that I add "review" or "sucks" (can work fine in combination with a specific product; negative reviews often tell you more about a product than positive ones, just like a requirements document or a product road map becomes a lot better if one includes things that people might the product to do that it will not do)