From what I've seen of Dawkins his vehemence & intolerance is the realm of science. If something can be measured he wants to measure it. A lot of his hostility stems from the theory of "intelligent design" which makes predictions about the world. Real world data can be gathered and when they don't match these predictions the theory needs to go.
Narrow-mindedness. He doesn't accept something as a truth without seeing evidence for it. On the one hand that could be seen as narrow mindedness. On the other hand observation and evidence can change his mind on any subject so in that sense he is not.
Science is the art of observation. First with unaided eyes, then using tools like measuring implements, microscopes, telescopes and today a whole crazy array of modern tools to aid our horribly inadequate vision. A lot of the poor religious science going around (e.g. creationism) is saying that the world is different to how it physically appears to our (aided or unaided) vision.
When people don't look he is saying to them "why don't you look?" That simple question is the source of the criticism which Dawkins receives.
He doesn't accept something as a truth without seeing evidence for it. On the one hand that could be seen as narrow mindedness.
Why did I say that? If that could ever possibly be narrow mindedness then it begs the question: What is open mindedness? If open mindedness would mean taking something as fact on word alone then it would quickly lead to inconsistency and nonsense.
"Well founded intolerance" is perhaps a more appropriate term to use in this context.
Note to self: Arguments with myself should be conducted internally - not on the forums.
I think the question he is getting most flack for would actually be "why don't you admit you see". Because practically every bigshot in creatonism or ID has probably been told and shown hundreds of times why exactly their claims are untrue, yet they just keep spewing their bullshit. And is it any wonder that Dawkins gets a bit crass when he has to endure constant willfull ignorance and dishonesty? I mean, the creationists and IDiots are still making claims disproved years ago.