also one should always be skeptical about the extent they believe they are not influenced by ads. that runs pretty deep. you say you instinctively don't trust it. but when the time comes to buy something, you won't automatically steer yourself towards a product that you have never heard before just because you have not seen an ad for it. having some names in your mind, even them showing up when you do research creates influence.
Such a belief purports that the effect of all advertising is measurable. It clearly is not. For example, someone sees your ad and decides your company is reprehensible. They were not a customer and they decide to never interact with your company. It's not possible to measure this. Anyone claiming it is holds what amounts to a religious belief.
The "generates negative returns" is the next myth in this. Whether or not advertising generates positive returns is not relevant. You can't measure the return of advertising in the first place. Even if you could measure it, you should be comparing it to the opportunity cost of not doing something more productive with that money. Which you also can't measure. No one rationally proposes that someone spends a hundred dollars on advertising to generate $100.10 in revenue is somehow a good use of money.
YouTube in-video sponsorships are a different beast admittedly; however there is still some basic tracking through use of promo codes (Use code JOHN15 for 15% off). They can see a report of how much they spent on ads that mention JOHN15 and how many sales included that promo code -- if sales vs ad spend are significantly positive, it becomes simple math to determine how much more to spend on ads, or to discontinue them.
I suppose your point though was that it's not possible to track the negative sentiment generated by the ads (people who get annoyed and decide to avoid your company at all costs). That is true, but companies who rather go down the path of something trackable than an unknown shot in the dark.