This is something that I have seen thrown around a lot on atheist blogs, I think the original was from Dawkins, and my best guess is it was out of The God Delusion. I don't have the exact quote, but the idea is that good people will do good things and bad people will do bad things, but for good people to do bad things it takes religion.
When I first heard this idea, I was totally on board. Religion inspires people to do some terrible things, and worse, it gives them this righteousness that is hard to combat. How do you convince someone they are wrong when they think they have God on their side?
However, when I hear this idea thrown around now, I always think "there are other things that can make good people do bad things also". This became clear to me after the riot following the Sandusky child molestation scandal going public. Tons of students were supporting their coaches even though one of them molested countless children and the other knew about it and did nothing. I remember thinking those protesters were horrible people, but then I quickly decided that most of them were probably good people, they just happened to be doing a terrible thing. I thought to myself "what could motivate them to do that?" There is no religion involved here, yet these good people are doing bad things, so what is going on?
After having this sit on the back of my mind for a few months, I have come to the conclusion that there are a lot of things that can make good people do bad things: sports, politics, poverty, religion, any ideology really. I would argue though, that religion is the worst offender. It really comes back to having God on your side. If we return to those students rioting after the Sandusky thing, I would bet that with a little reflection, most of them have decided that they were out of line. At the very least, this idea could potentially get argued and many of them could be convinced. On the other hand, consider matters that involve God. God can't be reasoned with, there is no room for compromise. By definition, God can't even be wrong, no matter what he does. Add to that the fact that many religious people value faith and have a persecution complex, changing anyone's mind is going to be nearly impossible.
So back to the quote that started this post, do I disagree with it? Yes, but really only in a technical sort of way. Religion is not the only thing that makes good people do bad things, but it is the worst offender. It still seems like a valuable enough meme to spread around, but I have to admit, every time I see it I am irked just a little bit.