“In the minds of Christian apologists, atheists cannot rationally criticize the Christian god for immoral behavior if an objective moral standard does not exist. I haven't seen a good atheist comeback on this issue. Does anyone have a good, concise, bullet-proof comeback?” — Gary M.
The underlying argument here is that one cannot justifiably criticize something on moral grounds unless one accepts an objective moral standard; that only God provides such a standard; and that therefore atheists cannot consistently claim that the biblical God is immoral — not even when he commands genocide.
The idea that objective moral values depend on God is something that can easily be disputed, of course, and many have done so. That only God can be the basis of morality — and even that God can be a basis of morality — needs to be argued for before the above claim can be taken seriously.
There is, however, another assumption here that isn't quite as obvious, and which allows for an even easier objection to the argument. This is the idea that one cannot criticize something on moral grounds unless one believes in an objective standard of value. But that is a mistake, and there are at least two reasons why it's a mistake.
To begin with, anyone criticizing the biblical God may claim that she is presenting a problem that's internal to the Christian worldview. That is, she may say that, though she does not herself believe in the existence of objective values, the Christian certainly does, and the problem is that the Christian cannot consistently accept the immoral parts of the Bible. That this is a valid criticism can be seen from the fact that the question of apparent biblical evil is something discussed by the religious amongst themselves. This shows that, given their worldview, there is a difficulty here.
The second reason the above is wrong is more important, however. Christians who make the above argument assume that one who does not believe in an objective standard cannot reasonably consider anything to be morally right or wrong. But the fact is that there is a third alternative between, on the one hand, believing in objective values and, on the other, being a nihilist. Obviously, if I believe that values are subjective, I still believe in values — namely, subjective ones! Thus it is simply not the case that I should stop objecting to things I regard as immoral.
I have moral views which say that (for instance) torturing sentient beings for fun is always wrong. I may not believe that there is a fact, discoverable by science or by philosophical analysis, that corresponds to the statement “torturing sentient beings for fun is always wrong,” but that doesn't mean I wouldn't oppose such an action. In fact, I would oppose it with every fiber of my being.
Nor is this merely my subjective opinion. There is actually a great deal of intersubjective agreement on such issues. The vast majority of us are opposed to murder and rape, for example. And it is this kind of intersubjective agreement that allows us as individuals to intelligibly communicate with one another regarding moral questions. Thus, when someone claims that God is good, they presumably intend to say, among other things, that God does not approve of rape and genocide. It follows that the question of God's goodness, as that claim is usually understood, can be meaningfully discussed on a subjectivist understanding of morality. The supposed objectivity of values has nothing to do with it.
The religious will probably keep making the above argument until the Second Coming — in other words, forever — but the simple fact is that they're wrong to do so.