Well, I’ll give it a crack.
First off, I’d like to mention that I don’t think religion is the sole cause of evil in this world. There are way too many variables to try and attribute every bit of evil to religion.
That being said, I do think that religion has caused quite a bit of evil in the world, and here is why.
When a person believes that something written or told orally is absolute truth, and there is no amount of evidence that would change their mind, then it can be concluded they cannot be reasoned with. They are holding dogmatic beliefs that will remain unchanging, unless the change comes from within.
This is a problem for several reasons, the first being that the ability to use reason is the only real difference between us and dogs, rats, pigs, black widows, etc. We don’t act like “savages” because of our ability to reason with one another.
Once that switch is turned off, and information is pumped into a person, that person will operate in much the same way a robot would, trained to do anything the teacher (book, orator, etc.) desires. Now, suppose that this book, or teacher, says that anybody who isn’t the same race as they are should be killed. It is accepted as fact by the trainee, and since the ability to reason has been disabled, they cannot be bargained with. They will kill as they are trained.
Now, I realize many would argue that it is the person who is inherently evil, and there’s no way that one could trace back the person’s actions to religion. But when a specific set of beliefs leads to the same actions and outcomes over, and over, and over, one can safely assume that it is not the person, race, or social circumstances that cause these actions, but rather their faith-based belief system.
The worn out example that I will once again mention is Islam. Every day, more and more people are blowing themselves up in the name of Allah. If every person in the Middle East was raised as a Jain, this simply would not be the case.
One could argue that it is their social circumstances that is to blame. I can’t deny that it probably contributes, but there are many poor and uneducated parts of the world where people aren’t blowing themselves up in the name of Allah. In addition, many of the masterminds of horrific plots, such as 9/11, are very educated, and wealthy.
Now, replace the Quran with the Bible, and we begin to find the same problem. Discrimination towards homosexuals run rampant in our society. I’m sure there are many, even on these forums, who don’t think homosexual couples deserve the same rights as straight couples, and don’t think they should be allowed to marry. Such a belief can be traced only back to one text, and because of the dogmatic nature of the text, and the inability for such believers to reason, there is no way through discourse that one could be convinced homosexuals should be allowed to marry.
For centuries, and millenia, the same rule of thumb applied to other races and women. It wasn’t until the majority of the population gave way to reason that the oppression suffered was called to a close.
So essentially, the “evil” in the world that religion is responsible for is due mostly to its disabling reason in the majority of its believers. And if one individual who has been programmed to believe without question, without reason, is dangerous, one can imagine how dangerous large population of such believers could be, especially taking into consideration the natural human tendency to exclude those who are different, and treat them unequally.
In my opinion, faith based beliefs are responsible for the division of mankind. Politics are faith based beliefs. Religion contains many faith based beliefs. And many of the insane are cursed with faith based beliefs that they cannot escape.