The Golden Rule is the pinnacle of ethics. But it does not replace the other moral precepts; it presupposes them.
Imagine a man reasoning, “Do unto others as you would have them do unto you -- yeah, sure. I wouldn’t mind if that fellow slept with my wife; fidelity is boring, and possessiveness is old-fashioned anyway. Therefore, he shouldn’t mind if I sleep with his.”
In order to get the right results from doing unto other as you would have them do unto you, you have to want them to do the right things unto you.