the last one is the only real reason; the rest are really excuses to question his existence
(don't tell the others I said that, it's an atheist secret!!!)
So how does the pursuit of knowledge exclusively exclude the possible existence of God? From the misuse of religion by groups and individuals I understand but science has also been misused is such a manner so the real question remains.... why is it a necessity for some? I'm sure I know the answer from a psychological and sociological aspect, but most people don't want to know, they consider themselves above common human failings and don't like hearing that they aren't. Yup the social sciences are my bailiwick.
A fair question. Let's look at it from both sides:
If there is a God, in a way, that's a great thing! If we can establish a contact with him, we could ask him about the intricacies of our world and universe and complete the database of human knowledge!
Of course, if he isn't real, there's the underlying problem that there isn't an omniscient being to tell us everything about the world and universe. Obviously this is suboptimal for knowledge gain.
However, the underlying issue is that there really is no evidence for this God. We have no way to contact him even if he does exist, and he hasn't left any evidence of his existence on his planet. Why, then, do we suppose he exists?
What happens here is that we can give non-answers to all of life's questions. How did the world come about? God did it. How did life come about? God did it. Why does the climate change? God did it. How were the sun, moon, and star created? God did it.
Without any reason to believe in this God, we have attributed to him many things, many of which we now know about (evolution, for example). Fundamentalism in particular is anti-intelligence and anti-science because it goes against the whole idea of attributing everything to an omnipotent being.
Of course, your argument seems to be "Who cares?" I answer, everyone interested in the pursuit of knowledge should care. Because whether there is a God or not would affect our view of reality entirely.