Darwinian speculations?

One of the quotes Michael Behe showed at Monday's Darwin or Design? evening was the following:

"We should reject, as a matter of principle, the substitution of intelligent design for the dialogue of chance and necessity, but we must concede that there are presently no detailed Darwinian accounts of the evolution of any biochemical system, only a variety of wishful speculations" (Franklin Harold, The Way of the Cell, 2001, p. 205).

That's not to say Darwinism is necessarily complete nonsense; clearly it isn't. But it does mean you don't have to be completely barmy to consider the possibility that it might not be the whole story.

And it's worth pondering what this "principle" is that rejects ID "as a matter of principle".