It’s one of those platitudes they are taught to repeat. They think of it as the “Rubic’s Cube” of challenges… a real brain teaser. The technique is interesting because they use a theological term, "faith", and try to apply it to the scientific method which is devoid of faith and founded in evidence. Faith by definition is belief in the absence of solid evidence. Therefore evidence is the antithesis of faith, the opposite. They are like matter and anti-matter…they simply cannot coexist in one entity. Thus at face the statement is an exercise in the absurd.
There is overwhelming evidence that the Earth is very old as oppose to 6,000 yrs old as the biblical literalists believe; overwhelming evidence for evolution and none for Creation, nor an intelligent designer. Thus rejecting god/gods for an explanation for the species, or to reject a biblical time line for Earth’s age requires no faith at all.
Here's what eludes theists about this whole issue:
If we as atheists denied the concept of god simply as an arbitrary flat rejection, then indeed, it would be a decision predicated on faith. But, as thinking people, the rejection of a god concept is a result of accumulated evidence that support natural causes for the universe. Not just one piece of evidence, not just one theory, but multiple theories with vast amounts of evidence.
Since cumulatively, these natural, repeatable, and observable pieces of evidence contradict supernatural explanations that are devoid of evidence, it requires no "faith" to accept the natural explanation and reject the supernatural explanation. From there it’s a short step to testing and observing the ineffectiveness of prayer; the dearth of evidence for miracles, or reanimation of the dead, etc., etc. Pretty soon, without any agenda to defend, the illogic of god and supernaturalism becomes self evident.
That they can't fathom this simple reasoning, and thus keep rolling out the “it takes more faith not to believe” canard, I attribute to theistic mental block caused by the religion meme, or gross ignorance.
Science and reason neither demand nor require faith. They simply require examination of the data, the evidence, without an agenda that demands rejection / ignoring of any data/ evidence to keep it viable, which is precisely what theists must do to keep their faith