Counting the numbers of deaths on both sides of this argument is not in anyway a measure of morality. For many reasons:
1. "In the name of". Whilst it is true that some wars and persecutions have been carried out in the name of Christianity or islam or (insert religion here), it's clear that the main motivation has always been power, ownership and control with religion providing the excuse. On the atheist side, no wars have been carried out in its name but several totalitarian regimes lead by atheists have performed horrific genocidal acts. But again, this is the nature of power.
2. Quantum. Even if it was possible to add up the deaths on each side it would be meaningless without allowing for the efficiency of modern weaponry and population sizes. Deaths would need to be weighted averages proportioned over time. The absurdity of this calculation is evident when you consider what damage a few dirty nuclear bombs or a biological weapon could do in the USA in the hands of a few Islamic extremists.
3. You can't generalise to the particular. An individual atheist is as likely to kill as a Christian and equally capable of doing good. That's just a statement of the obvious. And, as has been asked several times but never rebutted "what moral act can a christian perform that an atheist can not?"
4. Time. Morality is not absolute - despite the claims of extremist Christians. Our attitude to death, torture, slavery, freedom, homosexuality, women, democracy etc has changed over time.
5. Developed Society. We have developed strong secular institutions that have largely replaced the religion regulation of bad behaviour, most notably the Law and by providing welfare services, education and health.
All these things have made the argument of who owns the moral high ground utterly redundant in modern societies.
I have one reservation. Some religious organisations are dangerous and morally corrupt. But we shouldn't judge all people who have religious beliefs by the light of their extremists.
No murder No anger No retaliation Commitment Forgiveness Love for your enemy
Its extremely hard to justify violence in the name of Christianity when you actually follow the teachings of Jesus Christ. So why do people do violence in the name of Christianity? The diagnosis is right here.
"Mans heart is deceitful and desperately wicked." - Jeremiah 17:9
"The imagination of man's heart is evil from his youth." Genesis 8:21
A great example of how a Christian should act happened in 2006 when a gunman broke into an Amish school in Pennsylvania and gunned down a group of schoolgirls. The gunman shot himself and left a suicide note that said that he was "filled with so much hate" against God. The Amish repudiate any form of violence because of their belief in the absolute moral authority of the person and teaching of Jesus. The Amish community offered only forgiveness in an act of nobility and dignity.
Edited by Portillo, : No reason given.
And the conspiracy was strong, for the people increased continually - 2 Samuel 15:12
Religious books where written by men, plagued by the same corruption the majority is power and dominance. So when someone needs to justify their actions they can always find a particular text that fits their want to assert power over others.
Blacks well they have the mark given by god to Cain they should be slaves, Women well they tricked Adam to eat the apple you can beat them with a stick no thicker then your thumb, Peasants well they come from the line of that Noa's son who laughed at his father for getting drunk it says in the bible they haveto serve us who come from the other 2 sons.......
The one with the moral high ground is the one who goes beyond his biological morality and does not only apply it to those close to him but all humanity.
Christianity, One woman's lie about an affair that got seriously out of hand