Throughout history people have used religion to justify all kinds of atrocities but was it because they believed in a cruel god? Or rather could it be that they believed in an ultimately just god and that being on the side of the just god meant that they were sure they were in the right? Couldn’t a belief in a ultimately good and benevolent god be used as an excuse not to intervene and help other people because god is good and everything is god’s will? When one is advantaged in society and believes in a good and just god it is only a small step to believe that all of his good fortune is deserved and those who do not have the same luck must be sinners.
The ancient Greeks believed in capricious gods who were not ultimately good and loving. They were powerful and played games with humans and the only response was to be grateful when they favored you. Belief in a cruel god that you must fear could lead to humility. Often when God in the Old Testament shows his wrath it is because humans have demonstrated the hubris of thinking they are divine. It is a forceful reminder that men are not gods and do not have all the answers. So perhaps going off and killing in a state of religious certainty is not a good idea.
My instinct is that a person who is inclined towards cruelty will interpret religious narratives in a cruel way and a person inclined towards compassion will interpret those narratives in a compassionate way. And as circumstances and contexts change different meanings in an old text will spring to life.