April Fools' Day: The Atheists' Holiday?

David wrote: "Only fools say in their hearts, 'There is no God.'" (Psalm 14:1 and 53:1, NLT)

What was David talking about here? What constitutes a fool in God's eyes? Does a belief in God make one wise?

Webster's Dictionary defines an atheist as "a person who believes that there is no God."

With that definition in hand, I can think of a good many atheists who would be characterized by most objective observers as brilliant (e.g. Isaac Asimov, Andrew Carnegie, Sigmund Freud, Mark Zuckerberg, Thomas Edison, Richard Dawkins, Christopher Hitchens, Mark Twain, Stephen Hawking, etc.) We could quibble over whether some of these people are/were atheists or agnostics (doubters), but the point would still remain that a large number of "smart" people have stated or implied that God does not exist.
So what did David mean when he said that people who say that there is no God are fools?
In beginning to answer that question, we should note that context is always important if one wishes to truly understand any scripture. People have a tendency to focus on one part of an expression or verse. Hence, a closer look at these verses in context (and in conjunction with a few found elsewhere in the Bible) will better reflect the point that David was making here.
In the psalms quoted above, David wrote: "Only fools say in their hearts, 'There is no God.' They are corrupt, and their actions are evil; not one of them does good! The Lord (God) looks down from heaven on the entire human race; he looks to see if anyone is truly wise, if anyone seeks God. But no, all have turned away; all have become corrupt. No one does good, not a single one!"
(Psalm 14:1-3 and Psalm 53:1-3)
Hence, when we read the entire thought, it quickly becomes clear to us that David is not singling out atheists for scorn. David is indicting the entire human race for its foolishness and wickedness before God.
As humans, we love to make ourselves better than each other. "You people don't believe in God, so you are fools!" "You don't believe, so you are not in our group." "Those of us who believe in God are better than those of you who don't believe in Him!"
By the way, many of the atheists mentioned above are guilty of the exact same thing! They characterize the faithful as being blind and ignorant.
For some reason (that's another subject), it makes us feel better/exalted to ridicule/put down those who believe differently than we do. In other words, exclusivity is a wickedness that most of us have engaged in more than once in our lifetimes.

Let's consider a few other scriptures in the same vein:
"Fools think their own way is right, but the wise listen to others." (Proverbs 12:15)
"The wise are cautious and avoid danger; fools plunge ahead with reckless confidence."
(Proverbs 14:16)
"Fools have no interest in understanding; they only want to air their own opinions."
(Proverbs 18:2)
"There is more hope for fools than for people who think they are wise." (Prov. 26:12)
"Those who trust their own insight are foolish, but anyone who walks in wisdom is safe." (Proverbs 28:26)
Christ said: "Ye have heard that it was said by them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment: But I say unto you, that whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, 'Raca,' shall be in danger of the council: But whosoever shall say, 'Thou fool,' shall be in danger of hell fire."
(Matthew 5:21-22, KJV)
James wrote: "You say you have faith, for you believe that there is one God. Good for you! Even the demons believe this, and they tremble in terror. How foolish! Can't you see that faith without good deeds is useless?" (James 19-20)

Do we really want to crow about our beliefs and ridicule others for theirs? Do we want to be like the Pharisee who thanked God for how much better he was than others? Or do we want to be like the publican who realized that he wasn't any better than anyone else and begged for God's mercy and forgiveness? (Luke 18:9-14) Which one of those individuals was a fool?