The most convincing argument against the existence of God (excluding deistic god concepts) that I can think of is the existence of pastors, priests, popes, scribes, and missionaries. No one learns about God directly from God, but instead, it has to come through intermediaries. Why would an omnipotent god who wants a "relationship" with humans never talk to them directly and only speak through intermediaries? Why would he wait for missionaries to tell people about his existence instead of revealing himself directly to them? Why would he need humans to write his "word" for him? He wouldn't. A real god wouldn't need intermediaries to speak to people (one of the most inefficient and unconvincing methods possible), he'd do it himself. The fact that humans are necessary to spread the knowledge of gods is very strong evidence that the gods don't exist, and in fact, are human-made constructs.
Clearly, you have been thinking. Very good. On the other hand, I think you have come to the wrong conclusion.
OK, let's take a few steps back and look at this world and system. Since it is a creation of God, let's try to see what is really going on.
One action God has made is that knowledge must be Discovered. Look throughout time. God isn't handing out answers. If God handed out answers, history would look much different. All the problems would be solved. Since wisdom in gained on the journey to Discover those answers, God isn't going to stop the journey. If religion claims God gave them the answers, why is a leopard changing it's spots? It's not going to happen.
Religion is mankind's attempt to understand God. How are they doing? Religion claims to have all the answers. They do not search to Discover. They rely on beliefs. Instead of searching for truth, they are satisfied with beliefs.
Religion values so many of the petty things mankind holds so dear such as control. Aren't they really using God and beliefs in an attempt to control the actions of others? Isn't the threat of Hell or the threat of an angry, wrathful, or unloving God no more than intimidation?
Sure, religion teaches some very good things on Love and Kindness, however what else are they teaching?
If you assume religion's answers are God's way and answers, are you not being corrupted by religion's ideas that a few beliefs make truth? Making conclusions based on stories of what others say God is doing can not result in Truth regardless of how the logic fits. Logic based on Real Truth is the only path.
If one really wants to find God, one can study God's actions or just how this world's system really operates. It will all lead to God. Science is walking toward God. It will take much time, however on their current path, science will eventually find God.
The first thing God pointed out to me is that mankind carries such a narrow view. Discovery takes a wide, intelligent view. One must be open to all possibilities. One must not assume. One must be open to the fact that Real Truth will not always be an agreeable thing. On the other hand, Truth will always add up and one can Discover the Genius behind it all.
That's what I see. It's very clear!!