Your statement here undermines your prior premise: "And, no I don't believe I'd feel any particular caring for others if I thought they were just animals. I think that, like many people, I'd just be selfish. To say what you believe doesn't affect your feelings about others is nonsense IMO. How would you know that if you don't believe in something?"
If everyone has faults but are still basically good and caring, then the idea that you would cease caring about people if you lost faith is undermined. It might be true that *you* could feel that way, but its self evident that such would not be the norm.
I used to be a Christian, so I know what it feels like to have faith, therefore I know that how I feel about people now is actually a *lot* more altruistic and caring than when I was Christian.
Per God giving everyone a moral compass, there's no evidence of this. And just as you called me out for presuming what's in your heart, I'll call you out on this--You have no idea what my motivations or reasoning are. Your claim is tantamount to 'You actually believe in God but just pretend not to' which is pretty offensive because it presumes superior knowledge about *me* than me.
Per your barbarians statement, society is not Christianity. Social behavior is a point of genetic adaptation for humanity. From a beginning of anarchy people would form social units for basic survival.
Per no crime or war if people are inherently good, this is undermined by my prior statement that people can have certain hereditary traits that undermine the essential social caring humans have, and also certain tragedies can undermine this as well.
Overall, I find the doctrine of us all being sinners to be deeply disturbing. It establishes two dangerous ideals: 1) Superiority to those outside the preferred group, and 2) That humans by default are cruel to each other. These are premise that can lead to atrocity.