Good and Evil, moral and immoral, right and wrong, these terms are all relative and change within cultures and across time.
Many cultures dictate that killing another human being is wrong. The punishment for doing it? Death. So, killing is wrong...unless...it is ordained and approved by that particular culture or legal system. This means that it is relative.
For something to be absolute it either is or it isn't. I find most things to be grey, not black and white.
People don't believe in God for a whole variety of reasons, not just because they are hedonists. That's silly. I've known a few atheists who had morals that put a lot of Christians to shame.
I think this is a good point. It is part of the reason that many non-religious people get so annoyed by the bible-thumping evangelical missionary types who always say we'll go to hell if we don't renounce our evil ways and follow the path of righteousness.