You're making a lot of assumptions about the nature of God. What if God is directly affected by what people think It is? Sure, that's not compatible with most religious "evidence" out there, but by your logic, the nature of God is not determined by what is written about It in any book.
As someone who believes in something I call "god" (lower case, mind you, it's not a person), but does not accept any written scripture as having more inherent worth than, say, the Odyssey (i.e., hugely important for its literary merits and cultural influence, but not fact in any way), it seems to me that there is no way to evaluate other people's beliefs. I believe in what seems right to me, on a basic level that I don't really know how to assess rationally. I assume that, for at least some other people, the same is true of their beliefs. If any such person doesn't believe in the same thing as me, that means that at least one of us is wrong. However, since all I have to go with is a gut feeling, and I don't think my gut feelings are objectively better than anyone else's, I cannot determine which one of us is wrong. So I go on believing in what seems right to me, and don't compare it to other people whose beliefs arise from a similar instinctive level.
But - since I cannot evaluate my beliefs relative to other people with a similar type of belief, I cannot see how I can evaluate it relative to people whose belief takes a different form. Maybe the right way to believe is to learn what to believe from a book, horrible as that may seem to me. And maybe the right way to believe is to believe really hard in what you want. Who knows? Not me. I will go on believing what I believe, and others will go on believing what they believe. If I am wrong, and some of those others are correct, then God will sort us all out in the end.