When there is not sufficient evidence to support a claim, the default position should be rational skepticism if the goal is to minimize the number of false beliefs and maximize the number of true beliefs one holds. A central problem of faith is that if it can form a reasonable basis for believing one proposition without evidence, why does it not also form a reasonable basis for believing a contrary proposition? By what means can faith be discerned to lead to true beliefs, when it can be used with equal effectiveness to support conflicting propositions? One cannot argue that faith claims can be rationally evaluated in any way whatsoever to demonstrate their truth, because once faith claims are rationally considered against alternative hypotheses, the claims are either 1) no longer held (in favor of an alternative claim) or 2) no longer based on faith (i.e., rationality forms the basis for the claim). Atheists maintain that there is no strong evidence for the presence of a higher power, which is why theists need faith -- to replace evidence. Ironically, many theists have the confidence to deny the existence of fairy tale creatures from other mythologies and cultures, and deities of other religions, for which there is likewise no strong evidence.
Not believing in fairies or Father Christmas is not an act of faith, because those who are making these claims have the burden of proof, and must provide evidence to support the acceptance of such propositions. Technically, disbelief of a claim, when evidence is lacking, requires less a statement of faith, in the same sense that 0 is less than 1. Definitionally, it doesn't make sense to say that disbelieving "takes more faith," as it doesn't require any faith not to place one's belief in unsubstantiated truth claims. An analogous claim would be, "Not playing sports requires more athletic ability than playing football." However, when discussing the faith required to be an atheist, it is helpful to point out that two basic forms of atheism exist, and each could be described as requiring different degrees of faith:
weak (or default) atheism - the position of atheists who simply fails to accept propositions for the existence of a god; requires no faith because no claims are accepted as true without evidence. The weak atheist, therefore, does not accept that absence of evidence for a god is evidence of absence.
strong atheism - the position of atheists who believe actively that there is no god; requires more faith because the positive claim that there are no gods is accepted as true without evidence. The strong atheist, therefore, accepts that absence of evidence for a god is evidence of absence.
An atheist may wish to bring up this distinction to derail the "Atheism is a kind of faith" argument, as most consider themselves weak/default atheists. Some theists, such as Ray Comfort, may try to make the claim that this category is actually agnostics, as they usually represent strong atheism as the standard atheist position. One can point out that atheism categorically is, without belief in any gods, and that both definitions of atheism fall within this broader category. If the theist refuses to accept the self-applied label of atheist, then the atheist can suggest that the theist is making a distinction without a difference, and that moving on with the conversation is likely more productive than further semantic arguments (Careful however, as the theist might use their subjective definition to formulate strawman arguments later).
A final point the atheist could consider is that religions assert that faith is a virtue, so it hardly makes sense to criticize the atheist for having as much faith as, or more faith than, the theist. A reasonable question to directly follow the theist's objection to this would be, "Does faith prove me wrong?" (as in "Does basing a viewpoint on faith invalidate it automatically?") If the answer is "yes," the theist is either admitting their beliefs are not faith-based, or that they are wrong according to this reasoning. If the answer is "no," the theist is admitting that faith doesn't distinguish between the truth of his or her beliefs and the beliefs of the atheist.