"There is nothing a man cannot do once he accepts [...] there is no God"
That's nonsense.
There is no moral justification for what he did without a god, and no, two wrongs don't make a right.
It really should be: "There's nothing a man cannot do once he accepts the fact that God will forgive him."
Yup, Christian "morality" is corrupt like that ... but that's not surprising given the fact that this god also condoned owning human beings as property, committed or commanded genocide, infanticide, ethnic cleansing, taking virgins as war booty ..