One of the best arguments against believing in God is that there so many varieties of religious belief.
This doesn't happen in science, where there isn't an Eastern or Western science. Nor is there a Chinese or American science. Because modern science deals with entities that are real, there's agreement on, say, how subatomic particles behave, or the equations needed to put a satellite into orbit.
A friend of ours recently overheard a conversation between two men sitting behind her while she was on a plane. It started with one of the men asking the other, "Are you a believer?"
Turns out he was, so they launched into a rather loud discussion about Christianity. All went well until friction arose after it was learned that one of the men was a Jehovah's Witness.
Then the conversation became rather heated. Is God a unitary being, or is God a trinity of Father, Son, Holy Spirit? Our friend said they argued about this question for the rest of the plane trip.
What this shows is that nobody knows.
Whether God exists. What God would be like, if God does exist. There's very little agreement among religions about God's nature. Even Christians disagree about what God is like. Mormons and Catholics have little in common other than faith in Jesus.
(I think they agree on this; maybe they don't.)
Now, I used to argue that there was a common denominator among religions. It just was necessary to focus on what mystics in various religions taught about God.
But now that I've left behind my true-believing days, I'm aware that what I was doing was selectively choosing evidence for commonalities between mystical beliefs, because actually Christian mystics have a very different take on what God is like than, say, Sikh mystics or Islamic mystics.
So the fact that religious believers can't agree about God's nature is pretty conclusive evidence that God isn't real. The god of the Koran is very different from the god of the Bible. And Buddhists don't believe in any god at all, along with Taoists.
As the familiar saying goes:
“I contend that we are both atheists. I just believe in one fewer god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.”