Mankind, since freeing itself from the need to concentrate only on the basic requirements for survival, has searched for a greater meaning to life, and particularly, death. Humans need to believe that self-sacrifice is rewarded, that evil is eventually punished, and that all of their efforts lead to something more than a total and everlasting death. Our intelligence allows us to explore the concept of morality; but we cannot simply accept it as a system that allows gregarious, predatory creatures to coexist: we mold morality into a complex methodology that is primarily based upon faith, not reason.
Over time, mankind's quest for meaning has led to the creation of innumerable religions; most of them practicing a form of anthropomorphism: creating a god in man's image. Giving gods human characteristics allows us to perceive, and identify with, something that is beyond our understanding; as well as reinforcing a feeling of superiority over other creatures. Unfortunately, these gods, being like us, are also subject to human deficiencies; such as hate, jealousy, revenge, and prejudice.
Religion provides an indispensable service to humanity by guiding and controlling people who may otherwise have no hope, and no cause to lead a moral existence. Conversely, religion is also responsible for murdering hundreds of millions of people; Christianity alone killed an estimated forty million people during the period covering the Crusades and the Inquisition. Sectarian beliefs present a significant paradox: a system that promotes a feeling of belonging to a group, and of living a righteous life above that of others who have not found the "true" path; is also a system that can lead to an authoritarian fervor which will destroy non-believers.
The sectarian paradox has been prominent in the history of religions that follow the "God of Abraham": Judaism, Christianity, and Islam; but is by no means restricted to them. Any religion that depends upon blind faith is subject to manipulation by its leaders: if there are no provable points within a doctrine, all statements believed by the congregation become "fact". This situation is not always negative, as modern Christianity attests to: Christians, as a rule, selectively choose to follow the commands in their Bible that are to their liking, while ignoring many of the other rules laid down by their god(s). Homosexuality, disobeying one's parents, doing any form of work on the Sabbath, and many more sins, were to be punished with death. God considered slavery a normal part of life, and laid down guidelines that established slaves as less than human. Women are to be subservient and fearful, and are as far beneath men, as men are beneath God. Christians, and to varying degrees, Jews and Muslims, have chosen to believe in a system contrary to what is written in their holy books; but this situation is certainly to mankind's benefit. The current state of these religions is far from static, however, and future charismatic leaders will alter the status quo, for better or worse. Even religions originally established on simple moral principles, such as Buddhism, have evolved into belief systems populated by mystical entities, and therefore have become susceptible to further negative change.
There is nothing seriously wrong with the vast majority of religious movements at this point in time, and people who are sustained by a particular belief should not have their faith disturbed. A religion that provides a person with a reason to be moral, whether through fear of punishment (Hell, "wrath of God", etc.) or mystical reward (Heaven, deification, etc.), allows that person to have a life with purpose; and the church's control serves to protect society from that individual's potential actions. We occasionally encounter people with a fanatical, even psychotic, devotion to a particular sect. Consider, that without the structured existence imposed upon them by their faith, these people could pose a direct threat to others. Religion succeeds in many areas where psychiatry has failed.
The major flaw in religion is intolerance: sects claim to be the only "true" religion, and that all others are misguided. Numerous faiths teach that other belief systems are evil, and are the enemies of God. Groups that preach acceptance of diverse opinions, still foster a feeling of superiority over those who "lack understanding". This sectarian position ranges from harmless, to murderous; and has fluctuated throughout history. The popular solution to this problem has been to insist that all people should belong to one group, whether it is one specific religion, or one point of view, such as atheism; but this will never happen. In fact, religions will continue to fracture into more and more groups, as has been the case for thousands of years. In reality, there are six billion different beliefs on earth, since every individual interprets life in their own way. Groups are formed due to similarity of ideas, not because of identical doctrine.
Gathering into clans is more an aspect of human behavior, and primate behavior in general, than it has to do with spirituality. Clans, as they form, develop a defensive position: the members will draw closer together when the group feels threatened. Such a reaction can become extreme; as demonstrated by some well known law enforcement confrontations with cults. When a clan grows large enough, it is likely to adopt a more aggressive stance; becoming aware that it is now in a position of power, it may attempt enforced conversion of others. The point of aggression has been reached by many religions in the past: Islamic jihads and Christian Crusades are major examples that changed the course of history. Although both religions are based upon Judaism, and all follow the same god, by different names, and the same basic Hebrew scriptures; Muslims and Christians chose different prophets. Both prophets, Muhammad and Jesus (Yeshua Ben Joseph), preached peace; but, later in history, the two movements grew to a point where they tortured and killed people who did not strictly obey their respective doctrines. Fortunately, as a religion increases in power and size, it is more and more likely to contain individuals who wish to be in command; to control the masses: this leads to divisions in the congregation. The resulting smaller sects are likely to shift back toward a defensive posture. If this pattern did not hold true, the world would be in a perpetual state of war; and holy wars are by far the most brutal.
To summarize, we must look at certain basic points. Humans are animals, and follow established, universal, natural laws. We band together because we are pack animals, and therefore instinctively obey rules that allow predators to form such groups; humanity sees these rules as morality. In nature, there are limits to the size of social groups; these limits prevent depletion of resources in a given area, and ensure diversification of the gene pool.
Man is a primary predator: meaning no other creatures effectively prey upon man. The balance in the animal kingdom is maintained through having primary predators control their own numbers. Alligators eat one another; bears eat the cubs of other bears; male chimpanzees, felines, et cetera: kill the offspring of other males.
The problem is that humanity is ruled by instinct, and our behavior is simply a complex manifestation of animal drives; but man does not want to be an animal: so he creates gods in his own image, and elevates himself to a position above all else. We cannot have it both ways; either mankind chooses to be beasts, and fits within the balance; or chooses to be more, abandons the instinctive drives, and finds a way to harmonize within the balance.