I think a devastating argument can be made against the God that Muslims believed revealed the Koran from what we might term “perfect being theology.” According to perfect being theology when one says “God,” God is thought to be the greatest conceivable being. There is no being that can be conceived of that is greater than God. In fact, if something greater than what we believed to be God existed, then that greater being would be God.
Now, the greatest conceivable being must possess what we might call great-making properties, namely moral perfection, omniscience, and omnipotence. For example, a God that is not omnipotent (all-powerful), such as in its inability and power to control, say, nature or the natural world, cannot be referred to as the greatest conceivable. In other words, in some sense this God would be subject to the physical universe. But surely God, if he exists, is supreme over creation. Moreover, a God that is not omniscient (all-knowing) in that, for example, there are facts in the world that he does not know also cannot be the greatest conceivable being. A being that is infinite in knowledge is greater than a being that is limited in knowledge. Further, a God that exists contingently is limited in that it must owe its existence to something else, and is even at threat of going out of existence at some point in the future.
Thus, quite rightly, if some individual came up to me and said that he is God, I’d reject his or her claim on the basis that human beings are limited, finite, contingent things. Human beings are limited in knowledge, power, and moral goodness, and cannot claim to possess great-making properties, and therefore be God. Thus, a being that is not contingent is greater than a being that is. This presupposition seems to be intuitively and necessarily true, since nothing can be greater than God, and therefore provides a sound framework through which we can understand these other gods of other religions. Now, this presents a problem for the God of the Muslims. Why? Because Allah is presented in the Koran as being overtly partial, for example, Allah does not love sinners and unbelievers:
Surah 3:31-32: “Obey Allah and the Apostle; but if they turn back, then surely Allah does not love the unbelievers.”
Surah 3:43-45: “He may reward those who believe and do good out of His grace; surely He does not love the unbelievers.”
Surah 2:277: “God loves not the impious and sinners.”
Allah’s love is thus conditional. Though the Koran does state that Allah loves those who are pure (2:222), who do good deeds (2:195), are righteous (9:7), and those who fight in his cause (61:4), it also tells us whom he doesn’t love; he doesn’t love transgressors (2:190), ungrateful sinners (2:276), the unjust (3:57), or the proud (4:36). So, Allah is not all loving, but rather conditional in his love. Think of how devastating this is for children. We would be morally repulsed at a parent whose love is strictly conditional. Such a parent would likely say that “I will only love you if you do X and Y, my love must be earned.” Such would no doubt create an emotionally unstable child. Thus, if Allah was really what we would call the greatest conceivable being then his love should be unconditional, all encompassing, and impartial. But it is not, thus Allah is morally flawed, and therefore cannot be God. A being that is morally perfect is greater than a being that is morally flawed.