There is a religious dogma has done mankind more harm than perhaps any other religious idea. The dogma in question is the Catholic idea of “original sin”. The doctrine of "original sin" was first developed in second-century Bishop of Lyon called Irenaeus. According to historians it was, in fact, developed as a tool in a long forgotten fight against Gnosticism. In the fourth century this ugly dogma was developed further by Augustine of Hippo.
This new dogma was soon eagerly accepted by the Catholic Church. This happened also because it was soon seen that it was a work of pure (even if evil) genius. This dogma was to became a very central tool in bolstering the status of the whole church.

The idea that every human being is a "sinner" the day he or is she is born is the idea in the concept of "original sin". A real strike of genius was to claim that one can be absolved and forgiven from this "original sin" only by the official Catholic Church. If one does not get their forgiveness, one will just spend eternity in pain and anguish in hell.
The ingenious part is that one needs not actually do anything harmful or even think really immoral thoughts to be a "sinner" who needs the forgiveness of the Church. A problem for the church is that most people are not especially wicked. Most people simply do not do especially wicked things for which they would ever need forgiveness of the Church.

Creating a meme that people are born as "sinners" is a solution to this problem. This meme has helped Catholic Church greatly in its fight for a total mental supremacy in societies it has got hold of though many kinds of historical coincidence. This control has been spread also through bloody wars of conquest and often also through the total annihilation of all competing religious ideologies in those countries.
Of course, there is a deeper side to this all. There is a biological fact that all humans are alike. All humans will have, for example, sexual urges when they mature enough. These sexual urges are quite similar as the sexual urges of all of the animal species. They have an extremely critical function for making sure that animals do reproduce, as those species that do not have such an urge are long ago extinct.

A Sistine Chapel fresco depicts the expulsion of Adam and Eve from the garden of Eden for their sin of eating from the fruit of the Tree of the Knowledge of Good and Evil.- Wikipedia

Sexual urges are not a big problem is societies where people are allowed to choose their sexual partners freely and central resources are owned communally. In such societies the taking care of the resulting offspring is also often a communal affair. This was the case in some Polynesian cultures, in which there was no ideas of seeing sexuality as something harmful.
Sexuality was quite universally restricted and controlled as one of the side-effects of the emerging idea of private ownership of central resources. In agricultural societies there emerged a distinct new need to label all not allowed sexual activity as something bad and harmful.

Catholic Church did tap into this strong tradition. Eventually every single human being will find out that he or she has sexual thoughts. However, they find out that these thoughts are forbidden by the rules that aim to create a total control over human sexuality.
This is inevitable as the total control of even of these thoughts is not a natural thing. It is an unnatural requirement that is culturally created. This process greatly enhances the idea of "original sin", as every Catholic needs to face the fact that she or he will have "sinful" sexual thoughts when he or she sees an attractive member of the opposite sex.

This happens even if a person has been raised as a good Catholic from day one and has never been allowed to receive any kind of information about sexuality. There is a need to control actual sexual acts in every human society to a degree, but Judaism, Christianity and Islam have benefited enormously from their new and, in fact, quite outlandish requirement to control even ones thoughts.
As a human is a biological entity, it is inevitable that no human can totally control his or her thoughts. All humans will have these forbidden sexual thoughts at some point. The big break for religions comes at this point. They have created the idea that having this kind of thoughts is a mortal sin which can be absolved and forgiven only by them.

Catholic Church has, in fact, created an automata that will supply them with an endless stream of repentant “sinners”. This system works as long as all sexual thoughts are labeled as a “sin”, even if they are never acted upon. A very important part of this process is blurring of the big difference that exists between thinking about something and actually acting. It just requires accepting the unnatural idea that even thinking about something is a similar act as doing it.
This mental process for creating the idea of "original sin" blurs away the fact that we can have millions of thoughts and ideas that we never act upon in all fields of life and a thought that is not acted upon simply does not exist for any other person.

(This piece was completely refurbished on 16th of November, 2012)

http://en.wikipedia.org/wiki/Concupiscence