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?
Someone using that example as a why still has to explain why its universal and any “better” than a contrary opinion would be.
Even in comparing two opinions on right and wrong assumes an objective standard. That objective standard has to come from somewhere, or it’s arbitrary and futile and invalid.