I have taken a leap of atheist faith.
Religious people sometimes try to give proofs of the truth of their faith—Saint Thomas Aquinas famously gave five in his Summa Theologica. But for many people, belief comes before arguments, originating in family, social and institutional context, in desire and need. The arguments are post-hoc rationalizations. This can be true of atheism as well. For me, it's what I grew up with. It gets by in my social world, where professions of religious faith would be considered out of place. My non-faith is fundamentally part of how I connect with others and the world.
The idea that the atheist comes to her view of the world through rationality and argumentation, while the believer relies on arbitrary emotional commitments, is false. This accounts for the sense that atheists such as Christopher Hitchens or Dawkins are arrogant: Their line of thinking often takes the form of disqualifying others on the grounds that they are irrational. But the atheist too, is deciding to believe in conditions of irremediable uncertainty, not merely following out a proof.
Religious people have often offloaded the burden of their choices on institutions and relied on the Church's authorities and dogmas. But some atheists are equally willing to offload their beliefs on "reason" or "science" without acknowledging that they are making a bold intellectual commitment about the nature of the universe, and making it with utterly insufficient data. Religion at its best treats belief as a resolution in the face of doubt. I want an atheism that does the same, that displays epistemological courage.
Kierkegaard defined faith as "an objective uncertainty held fast in passionate inwardness.” He recommended Christianity not because it was well justified, and not in spite of the fact that it was insufficiently justified, but because it constituted a paradox: "The eternal God had appeared in time and died." That's not just difficult to explain, he said; it is entirely contradictory. By any reasonable measure it simply cannot be true. But that's why believing it called for total passion over the course of a lifetime. Christianity was the best thing to believe in part because it was the hardest thing to believe.
If a believer rejects rationality in this manner, you aren't likely to persuade him by showing him that his reasons are bad; he admits as much, or more. There's no use having an argument with a person who rejects argumentation.
William James—himself an eminent scientist—pointed out that science rests on emotional commitment. "Our belief in truth itself," wrote James, "that there is a truth, and that our minds and it are made for each other—what is it but a passionate affirmation of desire, in which our social system backs us up? We want to have a truth; we want to believe that our experiments and studies and discussions must put us in a continually better and better position towards it; and on this line we agree to fight out our thinking lives. But if a … sceptic asks us how we know all this, can our logic find a reply? No! certainly it cannot. It is just one volition against another—we willing to go in for life upon a trust or assumption which he, for his part, does not care to make."