I guess a rational argument in favor of religion would be that morality is not a "fact-based" idea, but rather an effort to get people to act contrary to "natural" animalistic urges by positing a higher power...a "parental figure" if you will, to keep people in line.
It's not true that "animalistic urges" are just about "nature red in tooth and claw". What makes workers ant work so sacrificially for their colonies? What makes mother tigers take such tender care of their cubs, rather than just eating them when they are hungry? What makes elephants herd together to protect one of their own herd against a potential predator? What makes wolves hunt so cooperatively in packs and then share in the meal afterwards? What makes a dog sacrifice its own life to protect its owner and his family against a potential intruder? What makes meerkats puts their own lives in danger when they raise a loud alarm at the sight of a predator to warn the others in their group to get away?
I was reading a few years ago about a family dog in Alaska. A large bear had come into the house, and there were young children there. The dog, without hesitation, had attacked the bear, which probably weighed about fifty times its weight, and put up a fierce fight to keep it at bay as best it could. It survived for less than a minute, of course, before it was torn to shreds, but that gave enough time for the family to escape with the children.
Was this a religious theist dog? Would it not have known what to do if it hadn't read its scripture? Dogs have been known to do these kinds of things in other countries too- even ones which aren't Christian!
This idea that evolution is just a selfish survival of the fittest is an unsophisticated understanding of how nature actually works, which is far more complex. In nature, species which do not know anything about cooperation, loyalty, empathy, self-sacrifice, and yes, even love, are at an evolutionary disadvantage. These emotions are hard-wired into "normal" humans (which don't have things like psychopathic personality disorders, which are neurologic deficits like dyslexia or autism, except that they lack the brain centers for empathy, or "conscience"). Neuroscientists have even been able to map where some of the brain centers for some of these emotions lie, namely in the part of the brain called the limbic system, in neurons called "mirror neurons"- which allow us to empathize and "mirror" others' emotions to ourselves.
