The Hitler & Stalin argument
The argument that Hitler and Stalin were 'atheists' seems to be raised quite a lot.
However, the fact of the matter is that both these two sought a clerical carreer in early youth; which, at the very least, suggests the presence of some sort of childhood faith. Furthermore, both these two quit - or, rather, were expelled from - their theological studies (in both cases due to unruly, aggressive and conflict-seeking characters) to pursue artistic carreers; Hitler as a painter and Stalin as a poet. None of them were successful beyond the mere mediocre ability to craft some pieces of work that would be of little to no interest were it not for their infamous next (similar) choices of carreers: Politics.
It seems a little off target to suggest that either of these gentlemen were 'atheists'. In fact, it makes a lot more sense to suggest that they had issues with religion(s) on a personal level, because they were not recognised as the leadership figures they both perceived themselves to be by their respective faculties. The reasonable conclusion must consequently be that they were both damaged by religious ideas during their upbringing - which, interestingly, is also the case with a great many mass murderers and other very prominent evil-doers in history.
"The idea of God is the sole wrong for which I cannot forgive mankind." (Alphonse Donatien De Sade)