Razib asks.

An equally interesting question is why does God believe in us?

Yes, or why do some people doubt God's existence?

Okay, this is where I started to laugh:

...people are killing themselves in the name of an entity that seems manifestly implausible to me, and that requires some explaining.

I can only guess he hasn't studied much history.

'There is no "real" Islam, or "real" Christianity, there is simply the distribution of beliefs and practices of a number of individuals which exhibit ranges, variances and central tendencies. The average believer is then important, but sometimes minority practices are also important. Most Muslims are not terrorist nutballs, but my own interest is disproportionately toward the terrorist nutballs since their behaviors might result in my death or discomfort, or that of those who I care for.'

This quote jumped out at me as very interesting. It makes perfect sense for someone who does not believe in God to judge religion by examining the practices and acts of those who follow a particular religion. Speaking as a Christian, I think it is exactly true that God expects us to be His representatives in the world. And thus if we behave differently then He would have us behave, we are being false and deceptive representatives. To someone outside the faith, that looks precisely like "those people claim to be Christians, but look at them torture people who disagree with them. That must be what Christianity is about."

That's not to say, of course, that what God would want would always dovetail neatly with some majority human consensus of what is best. The point I think I'm trying to make is that I probably shouldn't say "what Joe is doing is not true Christianity--true Christianity is believing and doing X, Y, Z." Instead I should be able to say "what Joe is doing is not true Christianity. Look at what Bill is doing. He's living like a true Christian." And I should also be believing and doing--not spouting principles.

So I guess, in parallel, if Islam is truly a religion of peace, I would expect true followers to be saying, repeatedly, "those violent people are not followers of Islam. Let me point you at people living out the life of peaceful Islam." And then I should see those peaceful followers of Islam not supporting the violent ones, telling how the violent ones are not of the faith, helping stop the violent ones, and living out the peaceful life.

I see some of this; I see some people talking about Islam not being violent. I'm aware of Muslims in my community who don't seem bent on killing every non-Muslim. But I also see thousands of people attending mosques where violence against non-Muslims is encouraged, and I don't hear much about Imams calling out for peace with non-Muslims and denouncing the Imams who call for violence against non-Muslims.

An aside: there is always the potential for intentional misrepresentation (I want to make Christians or Muslims look bad, or I want an excuse, so I will attribute by awful act to Christianity or Islam).

"Why do people believe in God?"

They don't. Social conformity is a powerful thing.