Morality and ethics are learned behaviors that are distilled from societal mores. If "thou shall not kill" or some equivalent in another religion didn't exist, for example, I'd argue killing would be natural in society, and nobody would question it. That is why certain tribal and indigenous peoples performed human sacrifices and had various rituals involving bloodsport. To those tribesmen, killing is not something abnormal within the tribe. Why would killing someone from another tribe matter to them?
My biggest problem with secular thought and especially the "pop atheist" variety is that it seems to often lead to is=ought. Regardless of the reality behind any form of theism, theistic thought never accepted that equality. It's always posited that there must be a "better than the way things are now." Some secularists dismiss that as wishful thinking and a coping mechanism, but if so why bother building or doing much of anything beyond the simple core of eat, shit, fight, and fuck?
We have also never fully acknowledged what the Spanish, British, and later USA did to the native populations of North and South America in the preceding centuries. Yes it's true that disease did much of the work without anyone lifting a finger, but that's only true in the early days. Later on there was plenty of intentional slaughter including bounties to encourage it.
When I look at the way Twitter erupts into ideological witch hunts or things like the Qanon cult, I realize that we have not changed. If any of those mobs got actual power we'd see the same things repeated against whatever groups (real or imaginary) they hate. Civilization is a thin veneer.