Even if theism is a failure, it's still superior to atheism

[R00tKiT]

Exactly the characteristics of a fundamentalist: they think they have the one, true answer and nobody should debate it.

There actually are some topics/issues in Islamic faith or jurisprudence that only admit one true answer. You either accept the answer or you can no longer consider yourself a Muslim. Muslims take their religion seriously, call them "fundamentalists" or whatever you want. 

It's a bit like someone clearly showingyou  some math proof and that the result/theorem is necessarily true (given some assumptions), and then you get angry and say : what a fundamentalist way to see things ? can't this theorem be interpreted any other way ..? there must be some way to avoid the correctness of this proof

It's exactly the same thing in religion. Once you accept metaphysical assumptions about God's existence and the divine source of the Qur'an, you have to accept the logical consequences, you can't play fast and loose with the faith after that.

There is no 'correct' interpretation of the Quran 

There is, but I assume at this point that you don't really care to know more about the topic.