They delude themselves with the idea that the all of the worlds problems are due to theism, and the world would be far better off without it. They base this idea on the delusion that theistic worldviews have been responsible for all the worlds atrocities.
Yet they seem to have selective amnesia when it comes to all the atrocities that have been perpetrated by the many infamous anti-theistic atheist tyrants of the last century.
The inconvenient fact that they so often try to sweep under the rug is that in only half a century these tyrants were able to engineer vast massacres which totally out-killed all the religious atrocities in ALL OF HISTORY COMBINED!
Atheists can berate theists all they want, but their atheistic worldview is responsible for far more carnage than any theistic worldview.
They have no basis what so ever for rejecting theism as being responsible for war violence and atrocities. Their worldview has far more to answer for than theism.
The following text and tables were all accessed from http://www.godandscience.org/apologetics/atrocities.html
What percentage of these killings were due to religious democide? It is less than 3% of the totals. The surprising thing is that these killings occurred during a period of time when virtually all the peoples of the world were involved in some sort of religion. Here is the data for the 20th century:
Vox Day, in The Irrational Atheist, lists 22 atheistic regimes that committed 153,368,610 murders in the 20th century alone:
What percentage of this democide was due to religious conflict? It turns out that religious democide doesn't even make the top 20 (although I am sure there is some in the "lesser murderers" category. Still, the total religious killings is less than 2%. In fact, the top two killers were specifically atheistic states (which had never existed before in human history). Should atheism be blamed for more than 50% of the atrocities committed during the 20th century? The answer of course is No! If one examines the nature of the regimes that committed these atrocities (even the religious ones), the key factor is absolute power (see Figure 1, right). According to Professor R.J. Rummel, in the 1816-2005 period there were 205 wars between non-democracies, 166 wars between non-democracies and democracies, and 0 wars between democracies. Lord Acton's warning that "power corrupts, and absolute power corrupts absolutely" seems to be more than just a trite saying.