Anyone who's spent time talking to a Cultist of Gnu is going to notice that the gnus typically want to maintain two mutually exclusive positions at once.
1) They want to perpetually be in the position of 'skeptic' - as in, they only want to be on the offense in most conversations. They want to attack ideas, not defend theirs. You see this manifesting through the constant attempts to redefine atheism to mean 'a lack of belief in Gods', as opposed to 'a belief that God/god(s) do not exist'. The latter is a claim, and therefore something that must be defended - so it's something a lot of Gnus avoid dealing with at all costs.
2) At the same time, they desperately want to push the idea that God does not exist, that there is no evidence for the existence of God/god(s), that God is very unlikely to exist, etc. After all, they want to spread their idea - they are evangelical atheists. And to do that means convincing people who believe that God exists that, low and behold, God doesn't.
But you can't have 1 and 2 at the same time. At least, not in a consistent, intellectually honest way. The moment a Gnu decides to take up arms and advance position 2, they've sacrificed the ability to hold position 1.
That doesn't mean they won't try to get away with both. Lately I've had a conversation over at Vogt's site, which started off with an atheist saying that there was not sufficient evidence for God's existence. I said, already - what would be sufficient evidence?
There was some talk about how philosophical and logical arguments don't give us empirical evidence (put the 'So what?' aspect of this aside for now), but then the response was 'Well, what do you have?' I said, no, you said there's not sufficient evidence. So clearly you can tell me what would be sufficient, right? I mean, you'd have to know what sufficient evidence is to declare there isn't any.
So they bite. And of course, it's what you'd expect: God could make everyone stop aging all of the sudden. God could cure all cancer in the world and cure all the amputees at once. Etc, etc. If that happened he'd be convinced God exists!
I point out the problems. First, that's not 'scientific evidence', contrary to what they were saying. But more than that - they were asking for gaps. Amazing things that science couldn't explain. There would be their 'sufficient evidence for God's existence'. So, I ask - I take it you believe that God of the Gaps reasoning is valid reasoning?
They try a few bluffs. Incredulity. (Are you saying YOU wouldn't believe in God if that happened? I say, nope, I think that'd work as evidence. But then again, I'm not the one discounting gaps-reasoning.) Intellectual bluffing. (Well if you tell me that's God of the Gaps evidence maybe I'll just have to say that not even THAT would count as evidence, and that evidence isn't possible! I say, go for it - PZ Myers and Michael Shermer have already made this move. At least then you'll be honest that nothing could convince you.) The moves don't work.
So then they try turning it around - 'Well, if you want me to give you evidence that would show God exists, you'll have to define God for me and tell me what evidence you have!' I say, no thanks. I didn't walk in here making any claims - you did. Why don't you define God for us? After all, you clearly had an idea of what God is in order to make comments about the sufficient evidence. But that led to gaps claims. Now, what you can also do is withdraw your claim about the sufficient evidence. But I'm not here to prove God exists. I'm here to evaluate your claims. I've highlighted some problems.
This gets a few more Gnus wading into the fight, but they all just try repeating what the first atheist said. 'The evidence he asked for would so be scientific, because we'd see it and things we can see are scientific!' No, that's not sufficient, and the appeal here would be to our inability to explain things. 'But they would contradict our best scientific theories!' Sure would - this shit's been done before. It may well happen again. We're back to 'gaps as knowledge of God.' You're just haggling over which gaps will work.
Finally comes the Gnu who insists that I've been dishonestly manipulating the conversation because *I* didn't give everyone my definition of God to begin with, and I should be the one providing evidence for God's existence - not asking others to define God and give their evidence. I say, horseshit. We have a man here who made claims about God. I wasn't even in this conversation when he made them. 'Oh yes, well that was poorly considered on his part, but now he's learned his lesson and...' I ask, and he'll be withdrawing his claims then? It turns out that he can't evaluate the evidence for God's existence after all, because he has no idea what he's talking about? Or can he, and he embraces God of the Gaps reasoning?
And throughout, the whole thing becomes clear. They want, desperately, to be able to make claims about God's existence... but they do not want to be put in the position of having to defend those claims. They want to stay on the attack, but they want no burden of proof. The moment they have one, they're looking for every possible way to drop it, short of being put in the position of having to say they have no idea how to evaluate the claim. (Which, by the way, seemed to be an issue with the original Logical Positivists. As near as I can tell, their intellectual framework made questions about God utterly undecidable, but damn, they wanted desperately to be able to say God does not exist anyway.)
Part of what struck me about the whole conversation was how damn obvious their inconsistencies were, but how they clung to them anyway. They want to denounce the God of the Gaps, but they don't want to be denounced when they demand gaps as evidence for God. They want to never have a burden of proof, but they want to be able to make claims, even strong claims, about God's existence. And if you catch them in an inconsistency, they never consider 'Oops, I made a mistake, wow maybe I was wrong about this.' Instead it's more, 'How DARE you point out my inconsistency! That's supposed to be what I do, and my side alone!'
This is one of the easier inconsistencies to call Gnus out on. If they tell you God doesn't exist, ask for their evidence, their proof. If they say God is unlikely to exist, ask for the same. And when they inevitably squirm and try to turn the conversation into one where you're claiming God is likely to exist, don't let them. Be the one thing that drives them out of their minds: a skeptic who is skeptical of their assertions.