I would agree with you that if anyone can conclusively show that something or another could not have evolved that it would be a valuable finding. However, ID arguments notwithstanding, this hasn't yet happened. Evolutionary explanations have been given for all of the systems that ID has claimed could not possibly have evolved. Whether or not the evolutionary or design explanations are correct is the question. Absent a test for design, there's no good way to answer that question. Since the evolutionary paradigm is the accepted scientific theory, (this paradigm was the one that met with staunch resistance because of religious objections, BTW, not the design paradigm) the burden of proof is on the design advocates to show that the design explanation is in fact correct. Without a test for design, I fail to see how this is possible. Of course, outside of the scientific community, people are free to believe whatever makes the most sense to them. Within the scientific community, however, evolution remains the accepted theory.
Well, anybody can give an explanation, the point being the ID explanation has more evidence -- meaning the explanations as to how the flagellum evolved etc. have nothing to back them up whereas ID can at least argue from the experience of design.