If you ever wondered how atrocities could happen, like Mengele's experimentation on living subjects, or starving the Ukrainian nation in the 1930s, wonder no more. All of these things are possible because the perpetrators were able to undergo whatever mental and moral gymnastics they had to in order to avoid seeing human lives as something sacrosanct. The abortionists demonstrate this by the terrible euphemisms they've constructed: "unwanted growth," "tissue," "clump of cells."
Rejection of God is the fundamental starting point for this sort of thing. I see arguments from atheists all the time saying that you don't have to be a believer to be a moral person, and I don't doubt that there are atheists who lead moral lives, but what (to appropriate Nietzsche) is the genealogy of that morality? These "moral atheists" live in a civilization steeped in 1500 years of Christian tradition, and that tradition has embodied itself in the secular institutions of law, justice, etc. They're operating on theistic morality they've acquired by cultural osmosis, whether they want to admit it or not. When you pare it down to essentials, murder is wrong because God commanded us not to do it, and those who do it will be judged for it. I don't know how secularists can assert an alternate morality for why murder is wrong, without ultimately appealing to a higher authority -- yet by its very nature secularism rejects the existence of such an authority.