Morality in a subjective universe
Part of the sanctity of morality lies in a fact that we live in societies where all moral agents are roughly at the same level of power - defined as the scope and depth of possibilities. Because of this, we have a roughly symmetrical situation where people's interests lie in a harmony of action and organization, instead of coercion/fraud/violence. Trader Principle, non-initiation of force principle, and so on.
Statism is a perversion of morality and the social fabric precisely because it makes "obeying the government" equally or more important than following one's personal values, simply because the government, the ruling class, has overwhelming power. Religion is a perversion of morality for the same reason - the religion, institution, dogma is seen as overwhelming personal values in importance, and that moral factor is in itself manipulated by moral agents (priests, theologians, and so on).
If a god really did exist, there would be a moral agent with a power more overwhelming than either of these - the god. It would have infinite power ! In such a case, the sanctity of morality is destroyed as well, regardless of the intentions of this agent. It doesn't matter if the god is benevolent or not (which the Christian god definitely is not). The only way out of this is to argue that the god has limits to its power (ex. open theism), which reduces it to the level of a powerful alien. The material is that which is limited and defined : the non-material, the non-existant, cannot have limits.
But we can take this further. If God exists, then the universe is necessarily subjective to its will. That means that morality, being a material fact, would also be subjective. This nullifies all moral principles - since principles can only exist in an objective system - and therefore nullifies the concepts of good and evil. And this means that it would indeed be impossible for a human being to morally judge God. But that's because it would be impossible to morally judge ANYTHING, including the decision to be a Christian in the first place, making the whole Christian enterprise meaningless.
On the other hand, this might explain why Christians reject our human judgment of God and why they reify God as their moral standard. Once you accept the subjective Christian worldview, what other choice do you have ? God is now an infinitely overwhelming moral agent. Even an army can't compare to that !
God also has infinite moral responsibility. This means that when God condemns its creation, it is basically condemning itself. When God gives out pseudo-moral pseudo-principles (they are neither "moral" nor "principles"), it is trying to limit itself, scolding itself for not following its own rules in the past. In this scheme, there is no place at all for human life and human interests. To be a Christian is to negate oneself.