In order to secure reasonable justification for atheism, does the non-believer need to answer the faith defense for theism? Your typical atheist feels compelled to say something (negative) about believing in God on the basis of faith, but do they need to? The answer is no. The faith account of belief in God presents no challenge to non-belief.
When one has faith that something is true, they believe it despite inadequate or contrary evidence. No one would say that they have faith that their basketball team was going to win the playoffs if by all measures the team is vastly superior to all of their rivals. People invoke faith when the chips are down, when life looks grim, when they can’t conceive of why God would allow someone innocent to suffer, or when it doesn’t look like there’s adequate justification in terms of evidence. If we had ample, compelling evidence, then there’d be no need and no room for faith.
Reason is prescriptive. When there is compelling evidence in front of someone and they understand it, and it is clear that it implies a certain conclusion, then they ought to believe that conclusion. Suppose that Smith is a defendant in a trial where the prosecutors have shown video of Smith holding up the liquor store, they found the gun registered in Smith’s name with his fingerprints on it, multiple witnesses all testified that Smith did it, the store owner identified him as the robber, other witnesses heard Smith promising to rob the store the day before, and Smith’s alibi has been shown to be false. The jurors, if they are reasonable people, should convict him on the basis of the evidence. If they don’t, they’re being irrational or unreasonable, and they’re failing to fulfill their epistemic (and moral) duties. So when the right conditions have been met, the evidence prescribes belief (there can be lots of mitigating circumstances that we will ignore for the moment). When someone doesn’t believe under those conditions, then they are epistemically culpable or at fault. By not believing, they make an epistemic mistake that they should rectify.
But faith is not prescriptive. When someone chooses to believe in God despite the fact that the evidence underdetermines or even contradicts the conclusion, on what grounds could they maintain that others who haven’t done the same have somehow failed in their epistemic duties, or are rationally culpable? In what way could the non-faithful possibly being doing something wrong by not also having faith? A believer by faith simply has no grounds from which they can argue that others who don’t have faith ought to. They can’t criticize the non-faithful for doing something contrary to reason or ignoring the evidence by not believing. In not believing by faith, the non-faithful are seeking to accept only that which is supported by the evidence. What is the faithful believer going to say: “You’re not listening to reason! You need to accept the obvious implication of the evidence! All of the evidence indicates that you should believe on faith!!”
In order to secure justification for believing that there is no God one would need to seriously consider the best arguments that have been made for the conclusion that there is a God. Those arguments are at least prima facie grounds against the reasonableness of non-belief. Believing there is no God is premature until one has good reasons to think those arguments are unacceptable. But the fact that many people have opted to believe even though they acknowledge that they don’t have reasonable grounds for doing so presents no challenge whatsoever to the person who concludes that the reasonable conclusion is to disbelieve. If their belief is acquired by faith, then they can make no claim against the rationality of atheism. They have made it clear that reasons and evidence are irrelevant to them—they’re going to believe what they want and to hell with being rational. Rejecting the relevance of having justifications for beliefs leaves them with no leverage and no possible complaint against the atheist.
Many atheists feel compelled to respond when a believer says, “Well, I have faith that God exists.” The atheist will offer a variety of criticisms of believing by faith. But it should now be clear that justifying atheism doesn’t require discounting faith. Furthermore, trying to rebut faith is typically futile. The faithful have already implicitly (or explicitly) acknowledged that what the evidence or arguments indicate is irrelevant to them. By invoking faith, they have already embarrassed and made a mockery of themselves more than any thoughtful reasoned rebuttal could accomplish.