[But I can't prove that he did so with logical rigor. I hope someday some one will do the same job on the Guide that Chaim Soloveitchik did on the Mishna Torah. Before Reb Chaim people believed the Rambam was rigorous even thought it seems to be full of contradictions. Reb Chaim proved it is rigorous.]
However if someone would say, "Then, fine. Jewish values are subjective.-So what?
Then it will follow that if we all took an attitude of approval towards Adolf Hitler, then Adolf Hitler would be good. Beside this, there are other objections to subjective values. [See Kelly Ross, Michael Huemer, John Searle.]
I think it is important to note that to the Rambam [Maimonides], the values of the Torah are objective and not observer dependent.
[Kelly Ross does defend Divine Command theory but I have not gotten a chance yet to see how he does it.]
So in short my attitude about moral values is this: Moral values are objective. They are embedded in reality. They are not observer dependent. And they are known by reason. Torah is to help us to know moral values that we would automatically know if not that the evil inclination affects our reasoning.
[Some people think belief in some system or other is the most important thing. This is found by religious people of most denominations. That is they put faith in their system above what reason perceives as moral value. That is not my approach. And I think it is not the Torah approach either according to Saadia Gaon or Maimonides. But this faith based approach did become the universal approach of religious people across all spectra.