Fist off, there can ONLY be an objective morality WITHOUT GOD, for God always and everywhere is only an example of how there is NO OBJECTIVE MORALITY - since he kills anyone he wishes, as often as he wants, and commands his followers to do the same, all the time in fact. If there was an objective morality, then God would be bound by that morality as well.
In his book Euthyphro, Plato asked a simple question: if there is a real difference between “right” and “wrong,” then we must ask if that difference is “due to God’s fiat or is it not?” If good and evil are absolutes, we must determine if they are absolutes because God created them, or because they exist wholly independent of God. And if they exist independent of God, then where did such standards come from in the first place, and more importantly, why should we not use such standards to judge even God?
If God created the standard, then God can only be as “good” as he is “evil,” because he would then exist and operate wholly outside of such a standard. Hence, the standard would only have meaning if God had deliberately created an existence in which such a standard could be applied. Otherwise, we are suggesting that God is powerless to change the very standard he is said to have created. Such a God would not therefore be all powerful.
If the standard exists independent of God, however, then judging God by such a standard would only prove He was worse than Hitler, Stalin, Mao, and every serial killer throughout history that ever lived, combined. In fact, God would even be convicted of having both the "mens rea" (the "guilty mind") and the "actus rea" (the "physical act") of both knowingly creating people that he knew would engage in murder, which is no different than creating a cyborg or a terminator, and sending it out on a mission to kill Sarah Conor.
In either case, an infinitely powerful God would, in theory at least, have the ability to create an infinitely better universe than the one we currently inhabit. God cannot be considered “good,” therefore, if every universe he creates is always only half as good as one he could have created. On the other hand, to suggest that God uses evil “to help advance his divine plan” is to suggest that God could not advance that “plan” without necessarily relying on evil. And that means that even "evil" is necessarily part of "God's plan." And thank God for evil! For If Jesus had been run over by a crosstown chariot or dropped dead from a heart attack, in other words, then humanity would never have been redeemed by all those who conspired to kill him.