You're absolutely right, people don't go to search engines to look at ads: they go to search engines to find the most relevant answers to their queries. In many commercial query cases, the most relevant/useful links could be paid search links that an interested advertiser thinks is super-relevant to your query, enough so to actually put down money to pay for you to click over and see their site.
"Most everyone knows that half.." - I think that statements needs to be qualified because as far as I have observed, only tech people approach targeted Google ads with this much skepticism that 50% of ads are scams and 50% are dubious.
I find that difficult to believe unless you are determined to disregard them. Especially when searching for a product to purchase, the best companies will advertise and often show a deal not obviously available in the search results.
"Most everyone knows that half.." - I think that statements needs to be qualified because as far as I have observed, only tech people approach targeted Google ads with this much skepticism that 50% of ads are scams and 50% are dubious.