Sam Harris

The most compelling explanation (that I've found so far) of what religious faith is comes from biologist Richard Dawkins.  His idea is that faith is a kind of virus of the mind. 

Dawkins calls "faith" a virus in an analogy with biological viruses.  They are both replicators in the Darwinian sense.  They use the information-processing capabilities of their hosts to make copies of themselves.  They use their hosts for their own purposes. 

The main thing for a virus is to replicate.  Doesn't that sound a lot like the middle-eastern religions?  Christians, for example, send out missionairies (who are themselves infected with the "faith" virus) to infect the minds of others.  Muslims want to spread their faith by any means (including war).  Muslims use the threat of death to keep Muslims from abandoning their faith.  This sort of thing is bad for the people, but good for the virus.

This idea is explained in detail in a chapter in Dawkins's book "The Devil's Chaplain".

Hi Tim, I agree it is a very good idea he has, and Dawkins is a most stimulating writer. He has a new book he is working on (The God Delusion) is the title I think. There are other excellent books out there for the lay reader, Michael Shermer has several books that speak to religion, and Pascal Boyer has a book called Religion Explained, I suggest you take a look at.
The short of it all is I think (because I dislike long posting, and that is why we have books) that human susceptibility to supernatural beliefs can be explained in terms of how human minds are wired, that is adapted to deal with the world.  Our minds, like everything else in the natural world are riddled with poor design. At the same time, we are still the same machines our ancestors were, we have the same stone age mentality, such as deference to authority. While these adaptations served us well 50,000 years ago, they are doing more harm today than benefit. As you rightly pointed out, religious ideas are like infectious viruses, and over time they have evolved. 50,000 years ago it was adaptive to believe in an afterlife where you were re-united with loved ones, I suspect it reduced stress and enforced community cohesion. But in today’s world, this is clearly not the case as Sam’s book shows us. 
Today’s religions are the megafauna of the world of ideas. Through competition with each other, they have become very powerful, and are all inclusive in controlling how a mind thinks about reality.  Most religious people I talk with are not stupid and incapable of reason, they simply cannot reason about reality as we can, they lack the mental tools to do so, their minds are hijacked by overriding religious notions.
Religion is like all other replicators in nature, the primary concern is not for the welfare of the vehicle but the spreading of the message. 
Science, democracy, and skepticism are our best weapons against it.