Originally Posted by Rotaerk

You are defining God to be everything which is good. First of all, good and evil are determined on a personal basis; they are not absolutes. Second, even if they were, defining God as such isn't very useful. People think of God as some kind of being, a metaphysical, all-powerful person, not simply another name for "good".

Now, on the subject of good and evil. "Good" refers to anything morally decent. "Evil" on the other hand refers to the extremity of immorality. So let's refer to the two sides of morality in general as "right and wrong". Morals are merely formalized rules which attempt to encapsulate personal feelings of what's right and wrong, of what you feel proud about doing, and what you feel guilty about doing. And of course there are morally neutral things, which leave no feelings either way.

You'll notice that there are tendencies for people to share similar views on what's right and wrong. One could blame this on evolution, culture, or God, but it doesn't really matter: They are merely tendencies, not absolutes. One does not need to believe in the existence of a God to have a moral compass. However, one does need to have a centralized system, such as a church or government, to enforce moral codes of behavior (such as the ten commandments or a nation's laws) in order to impose uniform standards of right and wrong.

Rationality is essentially making choices that are in your best interest. If you do not value the life of a child, then murdering children is not irrational, although the person with such morals would probably be considered a sociopath. For instance, if a person does not consider a baby alive at the time of abortion and thus doesn't feel guilty about it, abortion is certainly not irrational. Rationality is dependent on the person's sense of right and wrong, and more generally, on the person's desires.