What is moral? It is very simple, everyone knows (or should know) the difference between right and wrong).
For example, i know it is wrong to kill, certain religions have no problem with killing those of a different (or no) faith. In fact their holy books suggest their deity recommend it and is guilty himself. Jolly good way to teach morality... Not.
I think you are over simplifying it.
The problem with jumping to conclusions about what is morally right and wrong, at least in my opinion is that, so many things impact how we draw our conclusions.
So for instant saying that killing is always wrong, is clearly only if we are talking about someone that is innocent. Imagine being in a cinema or something and suddenly someone starts shooting at people, if you had a gun and shot this person, you would have done the right thing, and not only that, other people would probably also hail you and get you all over the news as being brave and a hero etc.
However have you mistakenly shot the person because you thought he had a gun, you would not only be considered a psycho, but also be thrown in prison for murder.
My point is that how one is perceived depends on what situation one find themself in. To me the difference is actually not that big from you being mistaken about the person and shooting him, compared to someone being convinced that human sacrifice will please the Gods and therefore bring good times.
In the moment you were convinced that you were doing the right thing, exactly as the shaman/priest whatever, being certain that a sacrifice is needed.
My point being, that we can only judge what is right and wrong from our own perspective, which is highly influenced by the culture and current situation we live in.
I obviously agree, that in general killing is wrong and if it can be avoided that is a good thing. But just want to make it clear that, being able to do immoral things are definitely not something one can point fingers at religious people for. Their scriptures in certain cases might add another layer and make them able to do immoral things that atheists wouldn't. But any immoral action or view as I see it, is basically just about conviction that we are doing good or bad. Which in the end is based on the current situation we find ourself in and the experiences we have had in our lives, mixed with some potential psychological issues.
And its probably possible to find some religious people, that wouldn't kill no matter what. Whereas I as an atheist, would have no issues blowing the head off a religious terrorist about to blow themself up among innocents.