Imagine talking to someone who attempts to justify the horrific crimes against humanity committed by Adolf Hitler or Joseph Stalin. What would you think of such a person? Even if they condemned such behavior today, their justification of brutal crimes committed in the past would not be excusable. You would look upon such a person with disgust and contempt and consider them incredibly immoral.
So let’s take a look at Christianity. Practically every version of Trinitarian Christianity, from fundamentalist to liberal, sees Jesus as the God of the Old Testament. To deny that Jesus is the God of the Old Testament is to deny the Trinity. If Jesus is the God of the Old Testament he is guilty of some of the most barbaric, horrific acts of infanticide and genocide known to man. Yet Christians of all stripes pray and worship this mass murderer of men, women, and little children.
Any Christian who refuses to condemn and denounce the God of the Old Testament is immoral.