Religious nominalism & cognitive opacity

I am a proponent of nominalism when it comes to religion. Or, to put it another way, instead of a religion being a Platonic category with precise and specific boundaries, I think a more accurate model is a distribution of ideas and sentiments in the minds of human beings which is always in flux. The many layers of cognitive operation, from reflective verbal commitment and elaboration, all the way down to reflexive and automatic conceptualization below the conscious surface, means that the shape of distribution the itself may change as a function of the level at which one is examining the phenomenon. While using the most reflective and conscious categories, those of self-identification and profession, may expose clean and sharp lines of separation between various religions, the lower levels may exhibit a great overlap and a relatively low correlation between a person's religious identification and their spiritual sensibility. In any case, with that preamble I thought it would be interesting to note this article in The Economist on "Islamic finance." Since most interpretations of Sharia place a ban upon usury, many "orthodox" Muslims have had to resort to "work arounds." For example:

New financial instruments are proliferating, from fee-based Islamic credit cards to Islamic mortgages, whereby the bank buys the property, then sells it at a mark-up to the client through an instalment plan. (The Saudi banking system, it may be noted, is largely interest-based; some contest the whole notion of "Islamic finance" as a mere sleight of hand, with interest payments called "profit sharing" and interest charges "handling fees".)

Now, as both a human and an atheist, I can engage in introspection and try to understand how one can engage in this sort of behavior. If God is omniscient would he not spy the real intent of something like a bank selling you a house on an "installement plan"? Never mind though, these sorts of "sleights of hand" are very common, even ubiquitous when it comes to religious phenomena. As an atheist who is interested in religion I have come to the conclusion that one must move beyond simple introspection to extract any value out of analysis of this subject. The nature of religion is riven with all sorts of such peculiarities and paradoxes. This may frustrate those of us who fancy ourselves "rational," but that is the reality of the world as it is and it does impact our own lives a great deal. If one models the mind as a community of impulses (or modules), not all of them transparently open to introspection, then one should be careful of how one rationalizes one's own decisions. Now, this reality should make us very cautious about relying upon such introspection to model the minds of those whose mental operations seem inexplicable or irrational to us.