The Bible does endorse slavery, but it is a different slavery that we know. The slavery the Bible endorses is debt based. If Bob is in debt to Steve, Bob works as Steve's servant until the debt is paid off or until seven years has passed. In this form of slavery, you are not property, you are not born into slavery, you are not physically abused, and you are given shelter and food. It is radically different than the slavery that the Americas experienced. As far as stoning disobedient children, there is no actual record of it ever being enforced. It seems to be more of a law to make children not want to disobey out of fear, but was never actually meant to be enforced. The Bible never says to hate homosexuals. It only says it is wrong, but please show me the Bible verse that says to hate them. The Bible seems to say the exact opposite of that.
Also in atheism, what kind of moral justification do you have to be able to call anyone bad? There is none. So an atheist couldn't even objectively say that God is evil because there really is no objective evil in atheism.
I would say that the Bible is inspired by God without flaw. Evidence of this would be that fact that there is fulfillment of prophecy from the Bible.