So what would you call me if I murdered your children and burnt you house down.
This agnostic would call you an insane vicious murderer. 'Sin' and 'evil' are Christian concepts, surrounded by layers of belief in God and the Devil. It appears to me you are trying to imply that atheists have no morality, which is an absurdity.
Taken to its extreme, the notion that people will rampage through the streets committing crimes without God beliefs to frighten them into good behaviour implies that you as a Christian are only prevented from doing such things because of your God beliefs.
Do you really think, if you lost your faith today, the first thing you'd do is run out and murder someone? Do you have murderous fantasies that only your beliefs keep in check? I expect not.
We are a social species. Social animals interact with each other in complex ways, and that interaction is the basis of what we refer to as 'morality'. So in that sense, we have indeed 'evolved' to have a sense of right and wrong.
Humans are not 'special' in this light. Wolves have strict social behaviours. They care for the alpha pairs' cubs, hunt together, socialise, have a heirarchal pack structure. But wolves, like humans,
can act outside their social rules. A very interesting example of this is a wolf pack, I think I recall in the US, where the alpha female was very vicious. She was found dead one day, and it appeared that the entire pack had turned on her and killed her, an atypical pack response to an atypically bad leader. I think there are obvious parallels to human 'good' and 'bad' behaviour to be seen in this incident and in others.