OK, so it's Easter and I'm reading all about the sermons being given by the various Church figures (at least those here in Sydney).
Archbishop Fisher says that Athiesm leads to Nazism, Stalinism, mass murder and abortion (Read article here)
Unfortunately this statement has no basis in fact. Terrible atrocities have been committed by religious and secular people throughout history. Religiosity does not guarantee moral virtue, and secularism does not guarantee moral iniquity.
Nazism was based on Christian ideology. Hitler regularly cited his Christian beliefs and that the rise of the German people was the "divinely-ordained". He cited Biblical references to the "brood of vipers" as justification for his Jewish pogrom. One slogan of the Nazi Party was "Gott Mit Uns" - "God With Us". Here's an impressive collection of Hitler's Christian references in his public speeches.
The point here is that being religious is no guarantee against committing atrocities. Pro-athiests cite examples such as Hitler, and pro-religious people cite atheist perpetrators such as Stalin.
Numerous psychological, political and social elements are required to engage in state-sponsored mass murder. However the absolute origin of these crimes is in the "us against them" mentality.
This divisive mentality can arise for numerous reasons - ethnic/racial characteristics, cultural differences, political ideology and (definitely) religious affiliation. Being secular in no way make you immune, but being religious almost guarantees you will adopt this attitude.
Most religions (and certainly the Abrahamic ones) authorise distaste, hatred and/or the slaughter of their opponents. The Bible endorses genocide frequently:
"Thus saith the LORD of hosts ... go and smite Amalek, and utterly destroy all that they have, and spare them not; but slay both man and woman, infant and suckling, ox and sheep, camel and ass." - 1 Samuel 15:2-3
It's not just the Old Testament. Jesus instructs Christians to slay non-believers (Luke 19:27). The Koran speaks of God's hate for the Jews and how he will turn them into monkeys (Surah 5:60 and 5:78).
If your goal is subordination of others then you'll find justification for your actions somewhere. Religion is certainly one place to go looking for it.