Due to its emotional impact, the evil God argument is very popular among atheists. A variant of this argument is the claim that Mary was only 12-14 years old when God impregnated her, therefore making God a rapist and a pedophile.
The first way to disarm this claim is to simply point out that there is no evidence for the initial claim. There are a grand total of zero reliable sources (heck, I don't know of any) that tell us how old Mary was when she got the very pleasant news that she had been selected to bear the very Messiah she and her fellow Jews had been waiting for. The Bible certainly does not. You will not find one verse that says Mary was any age, much less that she was anything other than a fully consenting adult.
In fact, when Luke records the event, he details Mary's reaction: A poem known as the "Magnificat" (Luke 1:46-55). This is a long string of praises to God, to whom she not only ascribes several positive traits such as mercy and strength, but even notes Him as her Savior, who had done great things for her, looking upon her humble state, and that all generations would call her blessed. None of this suggests Mary was, in any way, an unwilling participant.
Furthermore, as everyone knows, not only was Mary not raped, but she never had sex with any man, including her husband Joseph, until after Jesus was born (Matthew 1:25). It was prophesied that Jesus would be born of a virgin. Mary was confused as to how she could get pregnant as a virgin. Mary was a virgin. Therefore, God did not rape her.
So, we know that Mary was not physically immature. We know that Mary was entirely willing for this to happen to her, she even rejoiced in it. We know that God did not have sex with Mary, forcibly or otherwise. All of this is a lie atheists tell just to make Christianity look evil. But the greatest irony is, as much of an emotional impact as this argument has, it would actually fail, from a logical perspective, even if all of it was true.
See, the problem with moral arguments is they assume certain viewpoints to begin with. Of course, as a Christian, I believe rape and pedophilia are gigantic evils. This is because God has told us we are not to do these things, and even prescribes death for them in Theocratic Israel. Rape and murder, in the Old Testament, were identical in nature, and therefore identical in punishment.
But an atheist cannot say the same thing. In fact, they can provide no foundation for morality at all. Thus, they can say they don't like certain things, but they cannot say they are morally wrong. Think of it this way: If I was to point to things like abortion, homosexuality, porn, hookup culture, drunkenness, and all the other evil things we see in our culture, and say that because atheists tend to support these things, there must be a God, you would think I'd lost the plot. I can only call those things evil because God has said they are evil. Therefore, if there is no God, they are not evil.
In the same way, if there is a God, nothing He does is evil, because He is the source of all morality. That means even when atheists point to genuine examples of God doing something they don't like, it's not God being evil, it's them.
See, as much as we like to pretend we're in charge here, God owns this garden, and it's His choice which trees we're allowed to eat from. But if He wants to eat from the trees He has forbidden us from touching, who are we to tell Him otherwise? God is infinite in wisdom, there is nothing He does not know. God is infinite in love, there is no harm He wants to see us come to. God is infinite in authority, there is nothing He cannot think, say, or do, that we have any business questioning. And God is infinite in justice, meaning there is not one sin God cannot deal with.
In all of His Godliness, God has given us a particular way He expects us to live, and has decreed that death is the penalty for stepping outside it. However, He has also revealed that the death of the wicked brings Him no pleasure; He wants all to be saved and come to the knowledge of the truth. Therefore, while He owes us all death, He has provided an alternative through the child born to the fully consenting adult virgin woman, Mary. This child, Jesus of Nazareth, is God in the flesh, and He lived a perfect human life, never once sinning, nor even being tempted to do so. Nevertheless, He died the brutal death of a sinner, enduring a crushing beating before being hung on a cross.
But it didn't end there. On the third day, Jesus rose from the grave, and appeared to many witnesses. He promised salvation, everlasting life, to all who will repent of their sins, confess Him as Lord, and believe in their heart that God raised Him from the dead.