"Faith," in a religious context, does not refer to an abstract sense of hope or confidence but to a particular sort of belief - a belief in something not adequately supported by evidence. By definition, this is irrational (i.e., faith entails belief in something without sufficient evidence to justify the belief, and believing without sufficient evidence is irrational). But just because faith is irrational does not mean that those who are afflicted by it are somehow unintelligent or mentally ill. In part, this is because there are degrees of faith and most of it does not rise to delusional intensity. While strong and pervasive faith may indeed be delusional, the faith of most believers may be better understood as the suspension of critical thinking.
If we focus on so-called moderate Christians, we may find people whose faith is much less intense and inflexible than that of fundamentalists. Such Christians appear to be capable of compartmentalizing, setting aside certain aspects of their life where they are willing to suspend critical thinking and others where they are not. Even in those domains where they will suspend critical thinking, the suspension is not necessarily complete. Thus, they may still experience doubt, uncertainty, and the like, even when it comes to matters of faith.
One of the things that concerns me about such believers is their justification of their decision to suspend critical thinking in one case but not in another. They readily laugh in my face when I fail to provide compelling evidence in support of my claim that my neighbor's garden gnome comes to life, but they refuse to apply the same standards to their god belief. If god belief is somehow immune to any reasonable expectation of evidence, then who is to say what else should or should not be similarly immune?
We value reason because we know it works. Most religious believers agree with this and are perfectly willing to apply reason to most areas of their life. All we are asking for is a consistent application across the board.