Gods don't exists but the belief in them does and it actually does change those horrors from occurring, in real life, in the name of one's god. Without the justifications they found in the Bible and without their belief that the atrocities committed were favored by their god the Inquisition, Crusades, human slavery, most wars, etc. could not have happened with a strongly believed supernatural moral justification.
Any kind of god who could write such a mess of a book that is so contradictory and purposely confusing that to this day no one agrees with on meaning and then eternally punishes those who don't understand is no kind of god. Our morality evolves independent of gods. I bet what was accepted to get you into heaven 100 or 1000 years ago is no longer good enough today because we put our modern understanding of the world and advanced ethical ideas into play in order to interpret ancient holy books and make sense of the old gibberish.
Crusades were for power. Using God as the reason was to control the armies and force them to carry out the acquisitions. Slavery in the Bible is not the slavery of today. We have changed the interpretations of the Bible to fit today. It is necessary since very few people 'have as s es to covet', literally. To really understand the Bible, you have to interpret the meaning of the scriptures at the time they were written. Take 'profane'. In the original concept, 'profane' meant words spoken out side of church, therefore not sacred. It was not swearing.However, as time passed, profane morphed into profanity and included anything found repulsive by society.
(a.) Not sacred or holy; not possessing peculiar sanctity; unconsecrated; hence, relating to matters other than sacred; secular; -- opposed to sacred, religious, or inspired; as, a profane place.