I'm sorry, but no - the claim is that it is physically impossible for an irreducibly complex structure, as the flagellum is purported to be, to have evolved without some variety of intelligent intervention. That's straight from Behe (emphasis mine):
By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning. An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional.- Behe, Darwin's Black Box.
Ok, I'll go along with that modification with the word, "physically". But that's different from "logically possible" or simply, "conceivable". And the standard, it seems to me, should be what can reasonably be expected, not merely what is logically possible or conceivable.
Cordially,