The first point: if you are a Darwinian, what matters is reproductive success. The rest is mere froth. Forget God, faith and the other relics of a believing age. We are here to pass on our genetic heritage to the next generation. A person is just a gene’s way of making another gene. The bottom line is reproduction.
Second: Europe is the most secular place on Earth. Elsewhere religion is growing; in Europe it is dying.
Third: Europe is failing to reproduce itself. The fertility rate for stable population size is 2.1 (greater than 2 because some children die before reaching the age of reproduction). No nation in Europe has a fertility rate this high today. In France it is 1.9, in the U.K. 1.74, in Germany 1.37, in Italy 1.33, and in Greece 1.29. The average is 1.47. The native populations of Europe are ageing and declining.
Fourth: almost everywhere today on average, the more religious people are, the more children they have. This is true in Judaism, Christianity and Islam. The more orthodox the believers, the larger are their families. I suspect it is true among Hindus and Sikhs as well. The demographic revolution now taking place is documented in detail in Eric Kaufmann’s recent book, Shall the Religious Inherit the Earth?
Fifth: the greatest challenge to religious belief today is atheism based on neo-Darwinism. Hence the conclusion: if you are a consistent neo-Darwinian atheist you will wish there to be as few people as possible who share your beliefs.