Granted, almost all aspects of religion are equally irrational and divisive, creating huge rifts within mankind and society, but there is one aspect which I believe is responsible for most of the bloodshed and violence we see being carried out in it's name. And that aspect is the concept of an afterlife.
Most religions believe in the afterlife. Christians believe that only by selling your soul to Jesus and staying pure by doing fluffy adorable things in this life, such as not having sex and not paying $9.99 to watch other people have sex, will allow you to spend your afterlife ensconced in the velvety comfort of heaven. Otherwise, come deathbed, you will be banished to the hot frothy lava covered desolation of hell; or as non-Christians know it, Camden, New Jersey.
Muslims believe in an afterlife as well. Their belief is similar to that of Christians, except in their case, they feel they are better suited to go to heaven than Christians, by virtue of not being Christian.
Hindus are kind of confused about this issue. Their confusion arises from the fact that they are not really sure if afterlife consists of life in heaven, or returning back to earth as a different species. I think after realizing that there are about one billion Hindus on earth, many of whom would be heaven bound after their demise, in addition to the ten billion Gods and Goddesses already residing in heaven, they came to the conclusion that life in heaven might not be so great if, for every step you took there, you would be falling over a God's foot here and a swami's naked torso there.
That's why Hindus played it safe and announced that consequent to death, their tribe would be coming back to earth as a different organism, the type of which would be predicated by the amount of good the Hindu had done during his lifetime. For example, if you tossed a coin having heads on both sides and called tails just so that you could sacrifice your life and save your best friend from being killed by a dacoit, you would come back to earth as a human, and quite possibly, a well-endowed woman in the supermodelling business. However, on the other hand, if you spent all of your life drinking till you were 40, then suddenly woke up and decided that you wanted to spend the rest of your life bombing countries into oblivion, you would probably come back as an arthritic cockroach with kidney stones.
So as explained above, afterlife is a major belief in all religions. But why did it even come to be a belief and an integral part of religion? Well, long long ago when people were not as educated as we are today, when the accepted method of explaining any phenomenon was to say that it was a manifestation of God's presence, when people lived in communities ruled by, in most cases, a tyrannical leader, they started questioning the meaning of life. They already knew, that there was a God, but the question was, why was he being so nasty to them when they hadn't done anything bad or evil. And from that question came the obvious answer. That this wasn't the only life you were going to live. There would be a series of lives you would go through, so as long as you stayed strong and lived out this miserable life, you could be sure that another, much better life would be along soon.
But then that led to another question; If the poor, unhappy citizenry was going to get another shot at life, wasn't it unfair that the satanic king, who was the cause of all their sorrow would also be getting it? Hey, no worries, said the bright guy who came up with the answer. The king would have an afterlife too, but his afterlife would be spent trying to swat away demonic creatures with pitchforks who would torment him for all eternity. Aha, said the satisfied populace. That sure makes a lot of sense. Serves him right, the bastard. Thus, afterlife came to be a big part of religion.
This is the age of religious fundamentalism. Seemingly insane people willing to risk their own lives and limbs in the sole objective of annihilating others of a different faith. A thinking man would ask, why would someone spend their entire life indulging in murder and mayhem in the name of religion? What do they hope to accomplish, and wouldn't they be better off spending their short lives doing something more pleasurable like, say, plucking little yellow flowers in a grassy meadow in Vermont, or drinking till they puke? The answer, dear thinker is quite simple. They do not care about this life because they know that they are entitled to an afterlife of a better quality once they are dead. That is why they are so eager to let go of this life and move on to the next one. And that's why the concept of an afterlife is so dangerous, in fact, it is that aspect of religion that converts a harmless irrational fool into a deadly guided missile.
Secondly, the concept of an afterlife gives religion it's highly exclusionary nature. You look at your motherfucker of a neighbour who keeps banging on your walls when you raise the volume of your tv even a little bit, and yet doesn't have any qualms about playing loud rap music all weekend long on high bass. Damn, you think, I sure hope that guy's not gonna be my neighbour in heaven. In fact, you realize, just because he's being such a pain in the ass right now, he's gonna go to hell when he dies. Yeah, that's right buddy, lets see how your South Central attitude works in Lucifer's frying pan. And so, you mentally convert your neighbour into a lesser being, bestow upon him God's wrath, basically dehumanize him. Once that's done, you are just a Walmart away from buying a gun and cleaning his clock.
So you see, no matter how much one believes in God, no matter how devoutly you follow your religious rituals, or read your holy books, no matter how many virgins you sacrifice under the light of a full moon while dancing naked around a fire, that's quite alright. Because as long as you do not believe in an afterlife and realize that this is the only one you have and ever will, you will value it more, as well as the lives of everybody around you. And when you value life, murdering others or your own self ceases to make any sense. You might be superstitious, but you will not be a bloodthirsty fundamentalist.