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.
also i would propose that you should spend $100 on advertising (including cost of time reaching out to people etc) to generate $100.10 in profit(not revenue) if the return comes fast enough. you can estimate the opportunity cost of spending that money by seeing what interest rate somebody would loan you money for, if that .10% ROI is more than the interest rate on the money, then it's worth doing, even though it's only $0.10. then if you do need to do something else with the money you can take out that loan. I guess it might be harder to calculate opportunity cost of your employees time since it might take a while to hire more employees, but you can estimate that based on their hourly salary. also hard to calculate opportunity cost of your brand reputation from doing more advertising. and yeah hard to calculate opportunity cost of your own time but you can just estimate a hourly rate and good enough. most of the math is clear though and companies go on that. (disclaimer: i am not an expert on any of this)