Objective morality as a proper basic belief

[Amarok]

You can assert all day his nature is necessarily good .You have not established it necessity. And you have yet to argue why it should be accepted as good. Aside you proclaiming  that it's good . So on and  on the baseless proclamations go.

Agreed Jorm or as Michael Martin puts it

In any case, appealing to God's character only postpones the problem since the dilemma can be reformulated in terms of His character. Is God's character the way it is because it is good or is God's character good simply because it is God's character? Is there an independent standard of good or does God's character set the standard? If God's character is the way it is because it is good, then there is an independent standard of goodness by which to evaluate God's character. For example, suppose God condemns rape because of His just and merciful character. His character is just and merciful because mercy and justice are good. Since God is necessarily good, God is just and merciful. According to this independent standard of goodness, being merciful and just is precisely what a good character involves. In this case, even if God did not exist, one could say that a merciful and just character is good. Human beings could use this standard to evaluate peoples' character and actions based on this character. They could do this whether or not God exists.
Suppose God's character is good simply because it is God's character. Then if God's character were cruel and unjust, these attributes would be good. In such a case God might well condone rape since this would be in keeping with His character. But could not one reply that God could not be cruel and unjust since by necessity God must be good? It is true that by necessity God must be good. But unless we have some independent standard of goodness then whatever attributes God has would by definition be good: God's character would define what good is. It would seem that if God could not be cruel and unjust, then God's character must necessarily exemplify some independent standard of goodness. Using this standard one could say that cruelty and injustice are not good whether God exists or not.
This attempt to avoid the dilemma by basing objective morality on God's necessary character has another problem. It assumes that there would not be an objective morality without God. However, this seems to beg the question against an objective atheistic ethics. After all, why would the nonexistence of God adversely affect the goodness of mercy, compassion, and justice? Yet, this is precisely what would happen if being part of God's character created the goodness of mercy, compassion and justice. This point can perhaps be made in another way. One could affirm the objective immorality of rape and deny the existence of God with perfect consistency. There is no contradiction in claiming "Rape is objectively evil and God does not exist."[14]

And even if you argued for some source argument this will fail because

If goodness is not something that a god exhibits, but something of which the god is the source, the statement "god is good" becomes a meaningless tautology. Consider the property "tastes like an apple". Many things that aren't apples exhibit this quality, but what does it mean to say that an apple tastes like an apple? Nothing; it simply cannot be any other way. Similarly, defining god as the source of the property "goodness", then applying that property back to god, is equivalent to saying "god is consistent with his own nature", which tells us nothing