Christian God is usually defined as all powerful being, the infinite being or simply uncreated creator. Often he is described as totally good in the Bible.
1. There is no explanation for the existence of God
Some religious people have said that God is eternal and uncreated.
This is logically impossible, as eternity cannot exist and cannot be realized in any way. In fact, eternity cannot come into existence, as eternity by definition means "no end", so to come into existence, it would have to have an end. A logical contradiction.
For God to be eternal, past would have to be eternal, which is logically impossible, as with eternal past, we can never logically reach the present.
In eternity, number of causes would be infinite or there would be no cause at all, which in both cases would mean that there would be no actual cause to anything and things wouldnt need a cause in order to exist.
So God being eternal or timeless is impossible.
There is also no way to explain how eternity is even possible, as eternity by definition cannot be caused. So nothing can create eternity, making eternity uncaused.
As a result, there is no way to explain how God came into existence or why a different God or Gods doesnt exist instead.
But even if eternity was possible, it would work for atheism as then our world could simply be eternal and need no God.
2. There is no explanation for what causes God to do things
Why would God do anything? There is no reasonable explanation as to why God would create this world or any world. There is no cause which causes God to change, to act, to create. So a God would not create nor act.
3. The problem of perfection
A perfect being would create the most perfect world possible. Every part of that world would be perfect. Every rapist would be the perfect creation of God.
There is no explanation as to why the greatest and most perfect being would create a world filled with evil and non-perfections and random situations happening to random people.
Since each of us can imagine a better world, there is no logical explanation as to why a morally perfect and all powerful being created an unperfect world.
If you claim that this world is morally perfect, then you concede that every rapist is a morally perfect being.
Since world can only be morally perfect or morally unperfect, there is no 3rd option to save Christians.
So they must either concede that their God created a morally unperfect world, or concede that every rapist is a morally perfect being.
To make matters worse for Christians, they invented heaven.
Why would God put people on Earth, and then send them to heaven?
Why not send them to heaven immediatelly?
4. There is no way to justify punishing evil
If creating evil is a good action, then there is no way to justify punishing evil.
So God who created evil people would have no justification to punish them, as God himself creates evil.
Further, if creating evil is a good action, then all evil people are good.
5. Unjust disproportional world
Our world is filled with injustice and unjust treatment. In fact, randomly, good things happen to bad people, and bad things happen to good people, all at the completely disproportional random rate.
A perfect being would be perfectly proportional. Its creation would also be perfectly proportional. Why perfect being would create this random disproportional imperfection remains a mystery.
6. Disproportional punishment
Christian God does not follow "eye for eye" justice system that he said it should be followed in the Old Testament.
In fact, God of the Bible punishes majority of people with eternity of infinite pain of burning alive, when most of them didnt cause so much pain to anyone.
The punishment which God uses is infinitely disproportional to the sins committed, which contradicts the Bible's claim that God rewards according to deeds.
He punishes great majority of people with eternal great pain of burning alive, when those people in most cases did no such thing to anyone.
