Anyway reading through the comments left at the posting was an incredibly well-thought out and well-written response that I believe nails the phenomenon of religious communities.
Because this was a comment, I'll provide a link as well as including the entire text of the comment. Just know that this comes from a user who calls himself "phototaxi" and was posted over at UTI (http://brentrasmussen.com/log/node/199#comment-1030)
It is a mistake to think that religion persists, with all its breeding of intolerance and its fostering of bloodshed, because folks are deluded, whacked out and stupid. Not that these cognitive characteristics don't predispose to the acceptance of whacky, superstitious hoo-haw...
...but the real heart and staying power of religion comes from the community it creates. The latin root of the word religion is "ligere," meaning to bind together as strands of wheat into a sheave, and that is what religion does. The cognate goes through old French to inform the word "elite," as well, which is the perspective that belonging to a religion provides for its members.
Thinking about the persistance of religious structures in human groups around the world is illuminating. Why are some religions tolerant? Why are some proselytizing? And what are the characteristics of human groups that allow for the existence of hierarchies (generally composed of men) that depend on others of the group for all their resources, and produce nothing but metaphysical speculation and rules concerning behavior? Why has religion been so generally and spectacularly successful over at least the last several thousand years of human evolution?
One of the reasons is that in groups large enough where you don't know everyone intimately, religious injunctions lessened the threat group members posed to one another, while sanctioning depradation directed at non-group members. This is a recipe for the success of any group. The early religions were clearly local and tribal, and the evolution of successful religious ideas began at the time human groups began to grow and spread into regular contact with one another. Look at the god of the christians: he started out as a local animistic presence on an insignificant mountain in Sinai before obtaining promotion to creator of the universe and what-have-you.
As the development of agriculture and the domestication of animals occured, as trade and transportation developed, tribal religions came in greater contact and conflict. The stage became set for the selection of religious "memes," or ideas and practices that maintained the power to cohere a group when removed from the original local context. The meme for monotheism was very powerful. The "one god" idea kicked serious ass in its day, and is still kicking. There's a reason that the idea is enshrined as the first commandment.
Similarly, behavioral practices that seem senseless and random serve to solidify ingroup membership and identify outsiders and transgressors. Is there any real reason for jews to be unable to eat lobsters, for muslims to pray five times a day, and christians to partake of gluey little wafers and never say "godammit!" and etc, etc, etc? Well, yes. These things make one part of a community and the benefits--in principle--outweigh the costs.
The real problem with tribal religions in general is with their stance towards transcendent realities. Most religions claim some kind of divine provenance for their rules and beliefs, which implies they cannot be contradicted or individually transcended. In this sense, religious identity is a tribal identity. Tribal mores that persist, by definition, are tribal mores that perpetuate the tribe, even if those mores (like not eating lobsters) seems completely random or pointless. This is the source of the great conflict tribal religions have with post-enlightenment modernity: ideas like "individual rights," "democracy," and "objective science" threaten to dissolve the founding ideas of tribal religion. Individuals will become members of larger, more inclusive, and more successful groups based on supra-tribal identification.
Regarding the violence perpetrated with the sanction of religion: it is always against "outsiders," for obvious reaons (even when perpetrated against believers, those believers are first desanctified as apostates or heretics or whatever). No human group can avoid being replaced by another if it kills more than an incidental number of its own excess offspring, or if it gets outreproduced by a more successfully competitive group; similarly, no religion can survive if it fails to bind in new members at at least the rate of replacement (proselytize!), or if its members are outreproduced by believers in a different ideology (which is why tolerant religions tend to have fatalistic worldviews such as belief in "karma" and why in general intolerant religions are more successful).
The return to fundamentalism seen in the current monotheistic religions represents a return to the strategies that worked when it was just other gods whose asses were getting kicked. Unfortunately, now it is secularism and science and modernity in general that possess the threatening ideas which loosen the bonds of religious communities. There is a very clear reason that american mullahs are demanding the subordination of democracy to morality--seen in the demonization of homosexuals, liberals, and popular culture in general, and seen particularly in the battle against abortion and stem cell research. They idea that people can choose for themselves what is and is not moral is the death meme for traditional tribal religions.
To really squeeze the moral out of a long, long story, folks participate in religion because they believe it will protect their children and promote their success. All the other stuff is window dressing.
Responding to things (behaviors and ideas) that are seen as threatening to the kids are the lifeblood of religious groups. This is why the teaching of evolution is such a threat, and why fundamentalist groups must oppose its teaching to all students, not just their own. If kids who are educated are more successful than the children of fundamentalist groups, those fundamentalist groups will go extinct. The most effective response to ding-dongs like the Kansas School Board is for colleges to broadly state that kids from Kansas will be at a material disadvantage if they are illiterate and confused in basic science. Of course, the response of fundamentalists is to enlist twits like our current president and liars like Discovery Institute proselytizers to push for national acceptance of stupidity.
Fundamentalist leaders realize that their religions are in dire threat of extenction within a generation if they do not act against competing ideas. First, they specify the apostasy and heresy that is intolerable (homosexuality, abortion, evolution, liberalism); then, they sanction the ostracizing, demonization, and even killing of individuals, to get folks used to the idea. They embrace the killing of identified outsiders, and extoll the noble sacrifice of group members who die killing others. If they then have to sanction the killing of additional multitudes, well, they have history as their guide.