I think the point that VoiceOfRa is making is that, just as a non-religious person might reasonably think that killing a newly born baby is murder, so might a non-religious person reasonably think that killing a zygote is murder. If so, then whether religion has or has not contributed to more infanticide than lack of religion is irrelevant to VoiceOfRa's point. (VoiceOfRa, please correct me if I misunderstand your point.)
Also, it is not clear to me what you mean by "religion has contributed to more infanticide than lack of religion". If you mean that religion has contributed to more infanticides than have all causes of a non-religious nature, then that seems unlikely to be true (and hard to verify one way or the other). What is your basis for this statement?
I suspect the polymathwannabe is referring to the ancient custom of war where after defeating your enemy, you go around and kill all their babies and their males, and take their women. Of course, that has nothing to do with religion one way or the other.
Regarding ordinary infanticide, that was also an ancient custom, approved e.g. by Aristotle. The practice had nothing to do with religion but had practical motivations. Areas that converted to Christianity put a stop to it.
Another month, another rationality quotes thread. The rules are: