Defending the unfaith
Have you never heard of "if you scratch my back, I'll scratch yours?" What about "two heads are better than one?" There are many benefits to being concerned about others and happily cooperating with others. This is not just seen in humans. Females of many species help take care of other female's babies, despite not directly promoting their own well-being and happiness. Chimpanzees have been seen sacrificing their own life by jumping into a moat to try to save a fellow chimp, despite not being able to swim. An experiment with monkeys shows that when food was only available after pushing a button that delivers a painful electrical shock to another monkey, they would starve for days to avoid hurting the other monkey.
Of course a Christian would probably argue that apes and monkeys are not truly moral, since they do not obsessively try to regulate the sex lives of others of their kind.