once they believe in evolution, they're on the path to realizing God is unnecessary
This may be true in places like the US where creationism is strong, but not everywhere. For instance, for decades Christians in the UK have almost all accepted evolution, and most varieties of Christianity (even quite conservative ones) have no problem with it. That doesn't mean that there isn't any tension between evolution and those varieties of Christianity, but because Everyone Knows that the two are compatible, reading a good explanation of evolution won't necessarily make a Christian rethink his or her religious beliefs.
(I was a Christian for years and years, and so far as I can recall I never found creationism at all tempting. And when I finally got out of religion, evolution had very little to do with it.)
Seconded. Heck, even the Catholic Church says there is no conflict.
Today, the Church's unofficial position is an example of theistic evolution, also known as evolutionary creation,[2] stating that faith and scientific findings regarding human evolution are not in conflict, though humans are regarded as a special creation, and that the existence of God is required to explain both monogenism and the spiritual component of human origins. Moreover, the Church teaches that the process of evolution is a planned and purpose-driven natural process, actively guided by God.
In an Open Thread comment beriukay mentioned that he's reading C.S. Lewis' Mere Christianity. I've been reading it too, for interesting reasons.
In my case it so happened that I started discussing faith with a long-time online friend whose spiritual views I didn't yet know, and he turned out to be a Christian with a high regard for the Bible, who also has an interest in science. As our discussion turned to our readings on spirituality, I acknowledged (I think it was me) that I probably spent more time on books that reinforce my point of view than on books that challenge it, perhaps a case of confirmation bias. (I've been exposed to many poor arguments for Christianity, and dismissed them; but possibly that was largely a function of having started out with that bottom line already written and picking arguments I wouldn't have much trouble refuting.)
In the spirit of experiment we agreed to a "trade" - he would read (thoughtfully and with an open mind) a book of my choosing on reasons to doubt faith, and I'd do the same with a book he chose on Christianity.
So the idea here is to pick a book that's the "best argument from the other side" (as in quote 3 here).
I recommended The God Delusion - I'm not sure if that's the best choice given the above intent, but it's what came to mind on the spot.
Would you make a different choice? If so, what?