Do atheists accept that we Christians can be intelligent people? Nobody likes to be thought of as unintelligent. Anyway, to answer your question....
From my own perspective, I simply can't understand how anybody could be an atheist. I am being totally honest, here. I can understand how people can be angry with God, and I can understand how people can feel let down by God. But the concept of "no God" stuns me.
To me, it is so obvious that some being or other, who is greater than what exists in the material and non-material world, must have been the cause of what is here. If there was no creator, then there would be nothing. Everything that we see on earth, in the material realm at least, is either natural or created by someone. As I have said before, if I saw a Coke can sitting in the desert, I wouldn't immediately assume that it had always been there, or that it had created istelf, or that it evolved up out of the desert sand. I would know, from logic, that it had been made by a greater being than itself, and that the cause of it being there was by a greater being than itself.
From what exists in the universe, I logically conclude that something greater has been the cause of it. I believe that because life exists, therefore the something greater must have life. One cannot endow what one does not have. Therefore, the "something" must have life, and must be a "someone".
I also conclude, from what exists, that for there to be gradations of certain things like goodness, beauty, peace, light, justice, happiness, etc. that this greater creator-being must be the perfection of all of these things.
Anyway, because these things are so obvious (so self-evident), I cannot comprehend how anyone could not see them. Others may feel the same. This may be why you feel as though some believers in God don't treat you as having much intelligence. I am sorry that you feel that way. Many of the questions from atheists (on this website) show no respect for Christians at all, let alone for their intelligence.
As for what is so wrong about being an atheist, I suppose it boils down to what is expected, if we do acknowledge a creator God. I do, so I believe that is is an affront to God to refuse to acknowledge Him.
If, however, after careful, sincere, searching for the truth, you still cannot accept a creator God, then only God can judge you. I have no right to judge at all, and I hope that I can have the humility to NOT do so.
God bless. And peace to you, too.