In an otherwise unremarkable Q&A with Tufts atheistic philosopher Daniel Dennett in the New York Times Magazine interviewer Deborah Solomon says this:
Solomon: If we knew for sure that God existed, it would not require a leap of faith to believe in him.
Dennett: Isn't it interesting that you want to take that leap? Why do you want to take that leap? Why does our craving for God persist? It may be that we need it for something. It may be that we don't need it, and it is left over from something that we used to be. There are lots of biological possibilities.
Viewpoint: Yes, and among those possibilities is that evolution shapes us to conform our beliefs to reality. It would be odd if natural selection molded the human species to embrace with our whole beings beliefs which were radically at odds with the way the world is. It's not impossible, of course, but it's strange that Dennett doesn't seem willing to consider the possibility.
As to his question as to why anyone should want to "take that leap" - actually more of a step than a leap - the simplest answer is that unless one does take it one must admit that there's no meaning to life, no basis for moral judgment, no hope for ultimate justice, no basis for human worth, dignity, or rights, no reason to think there is an enduring self, no hope that those we love who have died are not gone forever, and indeed, no reason for thinking that love itself is anything more than body chemistry, no reason why we should trust our reason to lead us to truth, nor any reason why we should value true beliefs over false ones.
In other words, apart from taking that "leap" human existence is nothing but a depressing tale told by an idiot, signifying nothing. The rational response to a universe in which there is no God is hopelessness, despair, and nihilism. That Dennett himself doesn't wind up there suggests only that he doesn't follow his beliefs to their logical conclusions, no doubt because he couldn't live with those conclusions.
Someone may wish to "take that leap," furthermore, because they find the materialist explanation for the breathtaking fine-tuning of the physical universe and the astonishing organization and complexity of living things to be little better than a fairy tale. It may be that one takes the leap because believing that accident and coincidence, purposeless chance and unguided force, are responsible for creating structures and phenomena which even materialists describe as brilliant and ingenious, is quite literally incredible.
Solomon: I take it you do not subscribe to the idea of an everlasting soul, which is part of almost every religion.
Dennett: Ugh. I certainly don't believe in the soul as an enduring entity. Our brains are made of neurons, and nothing else. Nerve cells are very complicated mechanical systems. You take enough of those, and you put them together, and you get a soul.
Viewpoint: This is one way of looking at things, I suppose - the soul, life, emotions, and consciousness are nothing but atoms which have reached a certain critical mass and give rise to certain astounding emergent phenomena - but it's not the only way. We need not accept Dennett's dehumanizing reductionistic materialism, a view which, by the way, is thoroughly unscientific because there's no way to test it in order to grant that he might be right that there's no soul, in the classic sense, residing in persons.
It could be that the soul is not some gossamer, wraith-like entity that inhabits our body like a ghost-in-a-machine, to use Gilbert Ryle's famous metaphor. Perhaps instead we can think of it as the sum total of information which describes us as a person. It is, on this view, the totality of our history, our personality, hopes, dreams, loves, and fears. It encompasses a complete description of our physical, emotional, and moral selves. It is a comprehensive account of every aspect of our being all stored like a computer file folder in the data base that is the mind of God. As such it is eternal and indestructible unless God chooses to delete it. Even at the death of the body we have the potential to exist as long as God holds us (the information which describes us) in being in His mind. God may, if He chooses, reinstantiate us when our body gives out by downloading selected files from our folder into another suitable structure in some other reality.
Thus Dennett could be correct that we (our bodies) are comprised solely of material substance (I don't think he is, though, because I have my doubts that matter alone can fully explain consciousness) but he could still be wrong in asserting that there is no soul.
In any event, materialism of the sort that Dennett espouses is an existentially sterile view of life which people hold, not because they're compelled by science to accept it, but because it enables them to avoid having to believe in God, the concept of which they find repugnant.