One of the things "crazies" and cults do is take single verses or single sentences, decide that they are universal principles written in a literal and strict legal fashion, draw a series of conclusions, and ignore or rationalize away anything that contradicts those conclusions. Often, a single charismatic leader chooses which verses the group follows and which they ignore; this is the case with WBC.
On the other hand, a "reasonable person" will look at how different teachings relate to each other, consider the scope and context of each teaching, and try to build a coherent understanding of the whole. It's an iterated process; a study of passage A might change your understanding of passage B, while exposure to new historical or geographic information might change your understanding of passage C. Serious study, historical research, discussion, and reasoned, cordial disagreement (often of the form "I think you overstate the importance of X" or "I think you misunderstand the symbolism in Y") are characteristic of this approach.
To an outside observer who is not familiar with the whole of scripture, it's easy to slip into the misconception that both groups are making "flimsy rationalizations" or ignoring inconvenient passages. The only way to really clearly see the difference is to become familiar with the source material yourself.
Consider the prior analogy: crazies often believe they are standing on solid scientific ground, as they rationalize and ignore science that contradicts their ideas. To someone with inadequate understanding, it may appear that scientists also rationalize and ignore the crazies' data. With a strong enough scientific background, it becomes clear that the crazies' reasoning is flimsy while the scientists have solid, sensible, principled reasons for rejecting the crazies' conclusions.
> "faith in its current form is unreasonable?"
Faith, in the sense that a certain (rather vocal) Christian minority means it, is anti-reason. Despite your incredulous tone, faith, in its current and traditional form for most of the rest of Christianity, is reasonable -- as I said before, what it means to most of us is "acting upon what past experience has shown us to be true, even though present emotions make it difficult".
Your reference to "testing the Lord" provides a great example of what faith means. In Exodus 14, Moses leads the people to the Red Sea, where God lets them cross and drowns Pharoah's army; then to Marah, with undrinkable water that God shows Moses how to purify; then to the desert, where God gives them bread from heaven. Each step of the way, they whine about impending death. By now, experience has shown them that God is providing for them, so (per my definition above) they should have faith as a result of experience. Yet the next time they come to a place with no water, they again complain about impending death. It is at this point (Exodus 17:2) that Moses says "why do you test the Lord?"
They're not being criticized for unbelief in the unseen, but for unbelief when they should know better. They're not being criticized for wanting to see a sign from God; they're being criticized for challenging God for yet another sign. The expression "do not test the Lord" is always used in this sense -- when someone already has the experience to know better. (When people who do not have such experience ask God for a sign, He often gives it.)
