Religion actually does have an interesting role in human societies, one I've thought long and hard about (with a bit of help from Neal Stephenson, admittedly). Religion is a channel for rapid and efficient propagation of memes.
People naturally resist new information. Therefore, it's a struggle to get a population to adopt viable survival strategies in the face of established tradition that says otherwise. Take food sanitation for example. Early humans observed that eating pork had a higher chance than other meats to cause sickness. Since germ theory and genetic theory had yet to be invented, they had no way to understand that the reason for this is that the genetic similarity between pig and human allows for easy disease transmission. They needed a way to get people to stop eating pork, but nobody would do it just because they said so.
Enter religion. Insert "Because God(s) said ..." in front of any statement, and you automatically bypass the mental defenses of a properly conditioned population. Further, labeling it as "God's will" reduces the Chinese whispers problem — the risk of information loss in transfer — because people have a strong motivation (being called a blasphemer) to transmit the memes verbatim — especially in the millennia before reading became commonplace.
In short, religion is an extraordinarily successful (by evolutionary standards) means of transmitting cultural memes. It's no wonder it's stuck around so fervently. It also, unfortunately, is a correspondingly successful tool of political control, and by its nature it propagates harmful memes as readily as beneficial ones. People with the religion virus are susceptible to any
idea, good or bad, that is framed in the context of their existing beliefs.
Edit: I crossposted this here
as I suspect it may be more relevant.
edited 7th Dec '11 8:48:26 AM by Fighteer