[James C. Bennett]

Wouldn't you still have to have some other measure of "morally right" in order to judge the value and effectiveness of the tool in achieving it??

Nope.

The Golden Rule suffices. It cannot be reduced further.

If another was needed, that would supersede the Golden Rule.

Main point: No "side-features" that need to be ignored so as to use, a-la 1 Samuel 15:3

[D-fendr]

>>>The Golden Rule suffices

So if the question is:

Why is the golden rule morally right, the answer is: It just is.

No reason required.