People's being defensive reminds me of this from Chris Rock (being interviewed by SR) in Esquire:
SR: Like many nice Caucasians, I cried the night Barack Obama was elected. It was one of the high points in American history. And all that's happened since the election is just a shitstorm of hatred. You want to weigh in on that?
CR: I actually like it, in the sense that — you got kids? Kids always act up the most before they go to sleep. And when I see the Tea Party and all this stuff, it actually feels like racism's almost over. Because this is the last — this is the act up before the sleep.
I have my doubts about whether Rock is right about this, but he might be. If I wanted to make the case that atheists are defensive for this reason I would quote Nietzsche saying that the religious impulse is on the rise:
Why atheism today? — 'The father' in God is thoroughly refuted; likewise 'the judge', 'the rewarder'. Likewise his 'free will': he does not hear — and if he heard he still would not know how to help. The worst thing is: he seems incapable of making himself clearly understood: is he himself vague about what he means? — These are what, in the course of many conversations, asking and listening, I found to be the causes of the decline of European theism; it seems to me that the religious instinct is indeed in vigorous growth — but that it rejects the theistic answer with profound mistrust.
(According to Wikipedia this is Hollingdale's translation from section 53 of Beyond Good and Evil.)
Atheists often don't seem to like the religious instinct, or else to be incapable of distinguishing it from theism. Maybe when they perceive this instinct in non-theists they sense that religion will not die and react with anger. Or maybe it is religion rather than theism that they really dislike. Perhaps they really are evangelical positivists who value 'reason' and 'intelligence' the way the Tea Party seems to value 'freedom,' i.e. in a fetishistic, non-literal way, so that 'being rational' means rejecting anything as intangible as religion, much as 'freedom,' for some people, means something like 'USA!'.