It is my opinion that religion serves as a method of belief categorization. I could provide a lofty explanation with loads of detailed personal experiences here, but I wont for brevity's sake. In short, I believe that religion serves as a sort of badge that people use to either identify with or discriminate against one another. This statement is a given, but I believe that there is a deeper trend that follows beyond that. Becoming a member of a fraternity that was founded on the foundations of "Christian manhood" made me question the structure of other fraternities. After I had conducted some research, I realized that the vast majority of fraternal organizations, including both male and female groups, are founded on religious principles. I immediately began questioning other, greater organizations such as clubs, sports teams, universities, companies, corporations, and governments. This lead to the following hypothesis: given the opportune circumstances, it is possible that people who categorize others [based on religious belief] are likely to compartmentalize themselves into some of the aforementioned groups as a means to separate themselves from those they disagree with. This claim can likely be supported with neuroscience's discovery of mirror neurons and their role in the connective nature of the brain. Do you agree with this or not? If not, please pick out a specific portion of the argument that you disagree with so that I may clarify/defend my opinion.
The science of in-ground/out-group thinking and its role in cooperation and morality is pretty well understood (See, for instance, Teehan, John. In the Name of God: The Evolutionary Origins of Religious Ethics and Violence. West Sussex: Wiley-Blackwell, 2010)
That said, if I understand you, it appears as if you have it backwards.
Could you explain what you mean by "religious principles" in this context and justify your thinking that (even most but especially that the) vast majority of organizations are founded on them?
If you mean principles of doctrine and dogma that are explicitly religious in nature then, certainly not. But if you mean simply a set of beliefs and customs shared by the in-group then perhaps.
But where you seem to have it backwards is here:
[I]t is possible that people who categorize others [based on religious belief] are likely to compartmentalize themselves into some of the aforementioned groups as a means to separate themselves from those they disagree with.
People naturally fall into categories themselves given the nature of our evolved cooperative societies and our cooperative nature. Then, once in a category, we define ourselves by the features of the category– language, expressions, rituals, customs, dress, etc. This makes us able to easily and quickly identify members of the in-group. We evolved this strategy because if cooperation is going to be a beneficial adaptation you have to keep track of the cooperators and the defectors (cheaters). So we evolved to be adept at keeping track of the resources of our conspecifics and their relationship statuses (think of the things we gossip about). And because we often don't have the time with which to determine whether a particular person is an in-group member or not we look for those shorthand clues that can indicate whether the person is one of us. This is important because in-group members are likely to cooperate and not defect as in-group members while out-group members are not bound by the rules of the in-group.
So why I say that you seem to have it backwards is you seem to be saying that people compartmentalize themselves into groups as a means to separate themselves from those they disagree with (disagreement, then conscious and deliberate separation) when what actually goes on is that people disagree with others simply because they're not in the in-group (unconscious separation, then disagreement as a result of the that separation).
Anyway, I haven't the slightest idea why you would think that mirror neurons would play a role in this. As I'm assuming you know since you mentioned them, they're just neurons that fire when an animal performs an action and also when that animal watches the same action being performed by another. How that would figure into this, I don't know. Perhaps you could elaborate.