> I answered: Because layers must only be introduced if needed. Is there a need?

It might have gone better if you had also stated why that is the case, e.g. "every additional layer exponentially increases the likelihood of bugs being introduced, so their introduction must be worth that risk, or the higher cost of mitigating measures".

Of course, the challenge will still be that "likelihood of bugs" is rather abstract, and often people believe they can be prevented just by paying more attention, and assume that that will happen of its own accord.