We’re not talking about an instinctual reflex,
we’re talking about an abstract concept of good and evil, right and wrong.
The “why” of that is completely relevant,
because otherwise, any assertion of a standard is arbitrary, meaningless, and futile.
Ok, so if the why is relevant, is it still futile if the unbeliever accepts as his why the logical game theory argument? something along the lines of “adhering to the golden rule benefits everyone if everyone in society does it. I’ll start with me and lead by example.” Are there other “whys” that aren’t futile, even if they are in your opinion incorrect?