Many non-believers say they are agnostics rather than atheists. They do not think God exists, but they aren't sure and so are unwilling to call themselves atheists. A common attitude is: "Maybe there is something out there. After all, we don't know everything."
How sure of God's non-existence must we be to call ourselves atheists? Obviously we can't be 100 percent certain of anything. But we can be 99.9999 percent certain of a lot of things, and that is usually sufficient for making the decisions of everyday life. We can't be certain that we will not fall and break our necks getting out of bed in the morning, but we don't stay in bed all day because of this. We travel in cars and airplanes where the probabilities of survival are not 100 percent, but close enough to chance it. In these cases, we do a risk-benefit analysis and decide that the benefits justify the risk.
Some things are, for all practical purposes, certain. If we jump out of a ten story window, we can be pretty sure of banging ourselves up badly, not by the fall, as they say, but by the stop. Now, a plane with a mattress strapped to its wing might fly by under the window at just the right time to save us. Again, as they say, "anything is possible." But this is an example of the sorts of possible things we have learned not to count on.
So where is the border between agnostic and atheist? If we draw the line at 100 percent certainty, then we are leaving no room at all for atheists. In that case, we would have no atheists in a fox hole or anywhere else. Yet, some people call themselves atheists, including many who have spent time in fox holes. The word must mean something to them. I suggest that atheists are people who have evaluated the probabilities, done a risk-benefit analysis, and found that the existence of God is so unlikely that they prefer to live their lives without all the baggage that such belief forces you to carry.
The baggage of belief is heavy. Not only are you expected to donate time and money to your church, but, more importantly, you are expected to turn over your mind. And, as Dan Quayle has said, "a mind is a terrible thing to lose."
When you are a member of the faithful of any religion, you are not free to use your own best judgement on what is best for you, your family, and society. Instead, you are expected to defer to the judgement of others who claim supernatural authority. And since they can offer no real evidence to support their claim but their own word, you are asked to suspend your own intellect in the process.
Throughout the ages, many attempts have been made to provide a rational foundation for supernatural belief. All have failed. Preachers can still attract customers among the unsophisticated by logical-sounding arguments, such as: "How could all this - the universe, life, and mind - just have happened from nothing?" They then assure their listeners that God made it all. But consider the absurdity of the argument: Something can't come from nothing, and so it must come from God - who came from nothing.
Ultimately, belief in an undetectable, transcendent reality comes down to faith rather than reason. Churches have convinced the majority of the human race to believe in the unbelievable, to give credit to the incredible, to rationalize the irrational. An atheist is someone who can't believe in something that has no rational basis, that is nothing more than a fantasy and delusion left over from the ignorant and superstitious childhood of the human race.