Richard Dawkins famously defined faith as "believing despite the lack of evidence," a crime against reason that he imputed to theists of all stripes. I submit that this is a better definition of "blind" faith and, ironically, it's as common, or moreso, among naturalists (i.e. atheists) as it is among theists.
Consider three beliefs naturalists hold for which there is not a shred of empirical evidence:
1. They believe that life somehow arose from non-living molecules (abiogenesis) purely by chance.
2. They believe that the universe spontaneously popped into existence ex nihilo and uncaused.
3. They believe that there's an infinite array of universes (the multiverse) in addition to our own.
There's scarcely a shred of evidence for any of these beliefs but naturalists are firmly committed to them because to yield on any of them is to open the door to a non-natural explanation which brings them perilously close to theism.
Perhaps the most ironic belief naturalists hold is their belief that reason is a trustworthy guide to truth. I say this is ironic because naturalists also believe in the evolutionary story of the development of the human species.
A consistent naturalist believes that we are the product solely of evolutionary forces that have worked blindly and randomly over the eons fitting us for survival in the environment in which our ancestors found themselves.
This is a charming story but there's a serious flaw in it if one takes it too seriously. As philosopher Alvin Plantinga has argued, one can believe in evolution or one can believe in naturalism, but it's irrational to believe in both. Why is that? Lots of people do, don't they?
The answer is simple. According to naturalism, everything evolves to increase the prospect of survival of one's kind, thus our reason has evolved as a tool to promote human survival. But if that's so, then the function of our reason is to promote survival, not necessarily to find or discern truth. Sometimes, knowing the truth may lead to survival, but sometimes falsehoods may promote survival.
Consider an ancient patriarch who carries a genetic mutation that generates a belief that the more children one has the greater will be one's prospects in the afterlife. Such a man is likely to have many children, most of whom will inherit the gene and who will in turn have many children of their own who will possess the gene. The belief has enormous survival value for the gene which triggers it and will spread through the genome even though the belief is completely false. In like manner, our brains and its functions have developed to optimize survival regardless of whether those functions lead us to truth or not.
Thus if one believes evolution is how we got here, he really has no grounds for believing that his reason is a trustworthy guide to truth, especially about metaphysical matters. It may lead us there sometimes and it may not at other times. Since naturalism is a metaphysical belief system, it follows that one who accepts evolution has thin grounds for believing naturalism to be true.
The only basis for confidence that our reason is trustworthy is if we believe that human reason is somehow instilled in us by a a transcendent, rational mind which superintended the process, evolutionary or otherwise, by which we came to be.
When a Darwinian atheist complains that theists are irrational he's essentially acknowledging that he doesn't understand the consequences of his own beliefs. The irony is that he trusts his reason purely as an act of blind faith. Indeed, the further irony is that theists, the very people he indicts for being irrational, are the only people who have solid grounds for believing that reason is a trustworthy guide to truth.