"Why, in history, are there all the various attempts by groups to privilege their interpretation of reality and society at all and to impose it on others? From what does this 'need' [for lack of a better term due to my own limitations] come?"
I concur with an earlier response which cited man's need for safety. I think our very, very long period of dependence renders humans existentially anxious about safety and makes us compulsively seek safe structures/institutions. Put that together with fairly impressive reasoning and social skills and you have the ingredients necessary for the historically evolving construction of a man-made, artificial world to keep us safe and which is both our glory and our bane. The man-made world isolates/protects us from nature and makes us feel, paradoxically less safe. It's a vicious circle, in which the machinery of thought offers us both the possibility of protections and the projection of every-greater dangers.
Power (including its complimentary expression, as submission) is the short cut to safety, which we neurotically seek. This short cut is manifested in doctrines, group identities, privileged interpretations etc. The weaker the social and natural links that define relationships--as a safe base on which we can (dynamically) rely, the more potent the doctrines/group identities must become; this is why I am arguing that Capitalism, by eroding the social relationships that bind men, is the fuel for exacerbating the neurotic need for "fundamentals" to rely on -- whether this fundamentalism is expressed as respectable doctrine, like "theory," or in social practices that can be safely sneered at, like organized religion.
Joanna