Question about an objection to grounding objective morality in God that states that if God has a morally perfect nature, and he either engaged in or directly allowed genocide, slavery, and torture, then that means genocide, slavery, and torture are objectively good.

How would you address this atheist challenge to grounding objective morality in God: If God has an unchanging, morally perfect nature, and he either engaged in or directly allowed genocide, slavery, and torture, then doesn’t that mean genocide, slavery, and torture are objectively good?