Respectfully, educating stakeholders is part of your job. Until you accept and embrace that, you're likely to remain stuck in roles doing useless things.
If they heard from legal they need it and legal hourly rate is greater than engineering hourly rate, they will rather waste engineering time than spend legal time to save engineering time.
Attempting to educate stakeholders is part of your job. Forcing them to accept your reasoning may not be possible and they may have other reasons for their decisions that you may not know about or they may not wish to reveal (legal, marketing, internal politics, etc).
And at some point in pushing back, disagree-and-commit is the right thing to do.
Since the topic touches law, it's more complex to some people than you might think. To us it's obvious, but someone else might think that they better be safe than sorry and not get sued for accidentally setting a (non-essential) cookie somewhere without letting the user know. I definitely know some people who'd rather implement such "unnecessary" things than exposing themselves to a potential legal trap.
I would recommend thinking like a lawyer and writing a memo like one. Legal writing and analysis follows a very common pattern known as IRAC (Issue, Rule, Analysis, Conclusion):
(1) Identify the issue; (2) Quote all relevant rules; (3) Analyze the rules in light of your specific factual circumstances; and (4) Reach a reasonable conclusion based on your analysis of the rules.
This is how your company's legal team is making recommendations to management. You have to fight fire with fire. The only advantage your legal department may have over you is access to more comprehensive legal research services like Westlaw and LexisNexis. But at the end of the day, all they're doing is researching what the law is and how the courts are interpreting the law. Search for the right terms on Google, and you can do a pretty damn good job at crafting credible arguments. We don't need the lawyers always acting like they're at the top of the food chain.
You might instead consider asking people why they're asking, and figuring out ways to promote more widespread understanding.
Concretely: you might actively promote adblockers and tell people why they should use them. And rather than saying "we don't use tracking cookies", you could explain "here's why so many sites have cookie banners, here's why we don't".
I'm not suggesting doing it proactively; I'm suggesting doing it in response to the question, if people repeatedly ask the question. "No, and here are other ways to protect yourself" is stronger and more definitive than just "no".
Lawyers would argue that it might be a good idea to put up a sign if your neighbors have a dog that could attack them.
(weak argument but somewhat funny).
Lawyers are ultra cautious. If you can -guarantee- that no one is going to magically add tracking/google analytics or some such to your site than sure, tell them you don't need the banner.
