A true atheist is one who is willing to face the full consequences of what it means to say there is no God.
To say there is no God means among other things that there are no absolute standards. For instance, if you are an atheist who believes with all your heart that murder is wrong and you run into somebody else who believes with all her heart that murder isn't wrong as long as she can get away with it, there is no absolute standard by which it can be shown that one view is better than the other, just as there is no absolute standard by which it can be shown that vanilla is better than chocolate.
If you are an atheist who says that murder is wrong because it works against the good of society in general, then you are saying that the good of society in general is gooder than the good of the murderer in particular, and, having thrown out all absolute standards, you can't say that. All you can say is that vanilla is better than chocolate because you like it better and so do most of your friends.
If you say, "In the absence of absolute standards, I declare that murder is wrong in the name of common sense" then you have simply made common sense your absolute standard. What is in accord with common sense is right and what isn't is wrong.
What is American is right and what is un-American is wrong. What is ethical is right and what is unethical is wrong. What works is right and what doesn't work is wrong. These all bring God back under different names: nationalism, ethics, pragmatism. To be a true atheist is to acknowledge no rule except the rule of thumb.
Thus many an atheist is a believer without knowing it, just as many a believer is an atheist without knowing it. You can sincerely believe there is no God and live as though there is. You can sincerely believe there is a God and live as though there isn't. So it goes.
Lots of the time atheism isn't bad fun. I do what seems right to me and you do what seems right to you, and if we come into conflict with each other, society has human judges to invoke human laws and arbitrate between us. Who needs a Divine Judge and a Cosmic Law? We can learn to live in lower case.
Except sometimes. Sometimes it's almost as hard to believe God doesn't exist as to believe he does. I don't mean a baby's smile, which is probably gas. I don't mean the beauty of nature, which is always soon followed by the indifferent cruelty and ugliness of nature. I mean an atheist is about as likely as anybody else to walk into a newsstand someday and pick up a copy of the National Enquirer or some such paper. On the front page is a picture of a dead child. The bare back is covered with welts. The eyes are swollen shut. Both arms are broken. The full story is on page three if you have the stomach for it.
To be consistent with the atheistic creed, the atheist can say no more than that to beat a child to death is wrong with a small w. Wrong because it is cruel, ugly, inhuman, pointless, illegal, and makes the gorge rise. But what is apt to rise along with the gorge is the suspicion that it is wrong also with a capital Wthe suspicion that the law that has been broken here is not just a human law, but a law as immutable as the law of gravity, one by which even if there were no children in the universe and no grown-ups to beat them, it would be written into the very fabric of reality itself that such an act is wrong.
The atheist holds the tabloid in hand and asks the question, "Why should such things happen?" Atheism can reply only, "Why shouldn't such things happen?" But the atheist keeps on asking.
What makes it hard to be an atheist is the feeling you sometimes get in the pit of your stomach that there must be after all, mad as it seems, an absolute good in terms of which such an act as this can be denounced as absolutely evil. Thus the problem of good is a major stumbling block for atheism, just as the problem of evil is a major stumbling block for religious faith. Both must learn how to live with their doubts.
A true atheist takes human freedom very seriously. With no God to point the way, humans must find their own way. With no God to save the world, humans must save their own world if it's going to be saved. They must save it from themselves, if nothing else. A true atheist does not dance on the grave of God.
The laughter of faith in God is like Abraham's laughter when God says his ninety-year-old wife is in a family way. The laughter of faith in no-God is heard in Sartre's story "The Wall": A man is threatened with death if he doesn't betray the whereabouts of his friend to the enemy. The man refuses to do this and sends the enemy on a wild goose chase to a place where he knows his friend isn't. By chance it turns out to be the very place where his friend is. The friend is captured and executed and the man given his freedom. Sartre ends the story by saying that the man laughed till he cried.