Religious minorities serve a valuable function in allowing scholars and careful thinkers to distinguish religious from social and environmental factors in their analysis. If, to take a counter-factual, it were the case that all Muslims were Middle Eastern and all non-Muslims were not, then it would be unclear whether any given aspect of Middle Eastern society was related to Islam as a religion, or related to the type of government, or geographic factors, or anything else. One could reason about the nature of the causes, of course, but in the absence of disjunctive populations (the non-overlapping lobes of a Venn diagram), it would not be possible to test these hypotheses.
Fortunately, this is a counter-factual, despite the sloppy thinking of many who simply equate “Middle Eastern” with “Muslim.” In the first instance, it is a counter-factual because not all Muslims are Middle Eastern. Something that is true of Moroccans and Indonesians, for example, is more likely to be due to a common Islamic understanding than due to environmental factors distinctive to the eastern Mediterranean basin. Something thought to be “Islamic” but unique to the Middle East is less likely to be related to the religion. But the other half of the conditional is equally false: not all Middle Easterners are Muslim. If something is true only of the Sunnis and Shiʿites in the Middle East, then religion seems a more likely factor than if the same is true also for Jews and Christians in the Middle East.
For example, much of “Islamic” art is stylistically very similar to decorations in Christian manuscripts, which is not surprising since at least into the medieval period many of the workers producing “Islamic” art for elite Muslim patrons were themselves Christian. It was not unusual for Syriac manuscripts into the 20th C to open with a textual decoration resembling a monumental doorway, and the architecture of many mosques shared features in common with Middle Eastern churches from late antiquity onward. The distinctive Arabic calligraphic style, on the other hand, depended on the Arabic language and script, which most non-Muslim literate elites did not adopt until after the calligraphy had begun to develop in the medieval period. Now, however, it has been adopted by Christians as well as Muslims.
(Parenthetically, the existence of Christian groups outside of Europe also provides an opportunity for European historians to distinguish which aspects of their medieval culture were due to Christianity and which were due to the fact that the medieval European nobility were a barely civilized thug-ocracy. The Jewish population of medieval Europe can also play a disambiguating role analogous to the various non-Muslim groups of the Middle East. But that is for European historians to benefit from.)
Another example, this time from women’s history, shows that not even aspects of religion can be safely assumed to be explainable by religion alone. Women in medieval mosques were assigned to pray in the back, behind the men. There is a hadith in which Muhammad reportedly said that the best rows for women to pray in are the back ones, and the best rows for men are the front ones. Since these traditional sayings were considered normative in medieval Islam (or at least some of them, in certain ways), the case seems to be closed: the religion of Islam was the cause for women being relegated behind the men in religious services. But before we leave the subject, we might observe that in Christian churches in Iraq until the early modern period women were also placed in the back of the sanctuary, and two doors in the side of the church provided separate entrances for men and women. (Interestingly, the Bible was read from a platform on the gender line, while communion was consecrated at the front altar. I haven’t yet figured out whether women went forward to receive communion or whether communion was brought to the women’s side.) Now, these Christians were not likely reading the hadith collection, nor regarding it as normative. Is the gender divide of medieval Middle Eastern religious architecture, Christian as well as Muslim, due to religion, or due to trans-religious cultural assumptions regarding gender and space?
Failure to pay attention to the disjunctions in the Venn diagram leads to a disproportionate tendency among scholars to explain aspects of Middle Eastern society with reference to Islam. The result relegates non-Muslims to insignificance, but it does so due to an unarticulated circular argument. Only closer attention to Middle Eastern non-Muslims would allow scholars to discern the true significance and social effects of Islam.