I know some of you are probably going "Oh, please, where to begin???" But I do have a place where I'd like to begin: the book of Joshua.
In a nutshell, God decides that He'd like to give a wonderful "promised land" to His chosen people. I imagine that -- being God -- He could have used His omnipotent powers to turn the wilderness into a land flowing with milk and honey. Or perhaps He could have anticipated this and reserved a wonderful land for them (by guarding it with cherubim or something). Instead He chose to give them a land that was already inhabited: all the recipients had to do was massacre the inhabitants, every man, woman, and child. What a wonderful gift!
This story looks like a tale from a pagan polytheistic paradigm where the one tribe's God happened to be demonstrating that He's more powerful than the other tribe's God. But let's suppose this really is a tale of an act performed by the one and only God of all humanity. Imagine a child in one of the less-favored tribes -- terrified by the violence and pillage going on all around her -- desperately praying "Heavenly Father, please save my mommy and daddy and me!" and receiving as an answer "Sorry, I can't help you. The privilege of killing you and your family is a special gift that I've given to someone who will be arriving at your house shortly."
To me, this is far worse than the many instances in the Bible where God Himself kills people because this story teaches a deadly lesson: Check your conscience at the church door because God may command you to perform an act of unspeakable evil, and when He does, it is good and righteous to follow His orders whatever they may be.
To any Christian who says, "Oh, that's just the Ooooold Testament -- starting from Jesus, God is all peace-and-love," I'd like to ask the following:
Is this the same God you worship or isn't it? Do you believe He did this, or at least OK'ed this story to go in His holy book? If Jesus really changed things by fulfilling the old law, then please show me the Bible verse where God says "Remember when I told you to massacre the Hittites? And the Girgashites? And the Amorites? And give Me their treasure? In fact, that wasn't righteous at all, that was evil..."
I'm somewhat less worried about Christians who simply don't realize that this is in the Bible or just never really thought about it. But I am more disturbed by educated Christians who attempt to justify and rationalize this, and ask us to "look at it in context." Let me be very clear: There is no context where genocide is right. Even if God is standing right in front of you offering you eternal paradise as a reward for murder and hellfire if you refuse. There may be just causes for going to war, but "I want their land and my God wants their treasure" is not among them.
Now I realize that this harsh post appears to fly in the face of my usual claim of wanting to foster mutual understanding between believers and unbelievers. But this point bothers me quite a lot and presents a stumbling block in my own comprehension of the Christian mindset. (Same for the Jewish mindset and the Muslim mindset, by the way, if they also see this as a story of righteousness.) The whole story seems so incongruous with the ethics of the believers I know, and I'm at a loss to imagine what could possibly be going through their minds as they're reading it in their Bibles.