If G-d Defines Morality, How Could Avraham and Moshe Argue With Him?

If morality flows entirely from G-d, how could Avraham over Sodom or Moshe after the Golden Calf actually argue with Him?

Q. If G-d is the arbiter of morality, then how could it be that Avraham (Sodom) or Moshe (golden calf) could argue with G-d? One would think that whatever G-d suggests would, by definition, have to be totally moral and perfect. If Avraham and Moshe were right to argue, then where could they have gotten that sense of morality from, if not G-d?

Obviously G-d is perfect and the ultimate in morality. But part of that perfection includes His altruistically giving us the opportunity and free-will to choose to be like Him, and demand morality and good for mankind & how much more so, for our fellow Jews (as the famed R. Levi-Yitzchak of Berditchev often did). These are written for eternity in the Torah, to teach us how much more so we must stick out our necks and dare argue with man, including powerful and frightening kings or presidents, for the sake of Am Yisrael, whom our Father wants us to endlessly love and show unlimited mesirut nefesh in defense of our holy nation.