Just ran into this clip. Although this guy misleadingly equals christians and muslims his clip leads to some important questions and I'm curious to read your opinion.
1) Is G-d the only source of morality?
2) Can people disbelieve in G-d and be moral at the same time?
3) Where do you see righteousness in relation to theism, atheism and moralty?
These are important question. It is better to ignore what is theoretically possible and look at the historical track record. When the world was religious there were conflicts. Now that the world is largely secular, there are bigger conflicts. Islam is a special case and does not count in this analysis. Take a look at the greatest crimes of religion and compare them to the greatest crimes of atheist movements. There is no comparison.
50+ million died in WWII, nazism was entirely secular.
30+ million died in the Russian forced famines. Communism was explicitly atheistic.
80+ million died in Mao's China...Cambodia...North Korea...all atheistic.
Neitzsche was entirely right when he said that without G-d all things are possible. Unfortunately, he should have been more specific and said that without G-d, all horrible things are possible.