In the long run, culture like genes is to a large degree spread by reproductive success. Religions/belief systems that discourage reproduction eventually die ou

In the long run, culture like genes is to a large degree spread by reproductive success. Religions/belief systems that discourage reproduction eventually die out to be replaced by those that encourage it. All liberal/secular cultures currently have below-replacement birthrates, and hence will eventually be replaced by less liberal ones. So by the raw logic of evolution, it's very sane for religions to discourage lifestyles that lead to less childbirth, as to prolong their lifespan they need their adherents to keep having more children than adherents of competing ideologies.