One of the most common criticisms of belief in the Christian God is that it is mere wishful thinking. According to this view, Christianity is just an emotional crutch for those unable to deal with the reality of life without God, and those that are strong enough to do without religion should do without religion. (In response I would say by the way that this objection applies just as well to atheism as to belief in God.)
Second, if all that Christians were after were a comforting belief system, then they could do far better than Christianity, and there must therefore be some factor other than wishful thinking that makes them believe.
Christianity isn’t the Most Comforting Belief-System
If all that believers were after were a comforting belief system then they could do much better than Christianity. The Christian gospel, good news though it is, is not unequivocally comforting. The idea that if you believe in God then life’s a breeze over-simplifies the Christian experience.
Christianity does not teach that Christians get an easy ride; in fact, it stresses that believers may well undergo great suffering in this life. It also makes people aware of their fallenness, of their sinfulness, and that can hurt. For all the comfort that Christianity offers in terms of eternal security, even its teachings about eternity have a downside; many Christians face the painful experience of expecting close friends and relatives to face just punishment for their sins.
If believers were really just after comforting beliefs, then they could do a lot better than Christianity. For example, they could believe that suffering is just an illusion, that there are no moral constraints that oblige us not to do what we want to do, and that all (not just Christians) are destined to enjoy a blissful afterlife in heaven.
These beliefs, though, are all seen as heretical by the Christian church. Why? Because Christianity isn’t mere wishful thinking.