Today's Guardian includes an excellent article on Inscrutable Design by Richard Dawkins and Jerry Coyne. They thoroughly demolish the "teach the controversy" excuse for importing fundamentalist purportedly Christian intolerance into science classrooms.
Intelligent design is not an argument of the same character as these controversies. It is not a scientific argument at all, but a religious one. It might be worth discussing in a class on the history of ideas, in a philosophy class on popular logical fallacies, or in a comparative religion class on origin myths from around the world. But it no more belongs in a biology class than alchemy belongs in a chemistry class, phlogiston in a physics class or the stork theory in a sex education class. In those cases, the demand for equal time for "both theories" would be ludicrous. Similarly, in a class on 20th-century European history, who would demand equal time for the theory that the Holocaust never happened?
That last sentence is perhaps the most telling, because it actually goes to the core of what the Inscrutable Design advocates really mean. I am reminded of Atwood's Republic of Gilead every time I see ID advocacy, because in reality it doesn't even rise to the level of "argument." It is, instead, preaching—which has no place in a science classroom.
Part of the problem is the advocacy method adopted by ID advocates, beginning with the intellectual dishonesty put forth by and through Philip Johnson. Johnson, at the time he began his crusade, was a law professor concentrating in criminal law and evidence. That is precisely what the ID argument boils down to, with a few strange twists along the way. Basically, the ID argument requires that evolution be proven beyond a reasonable doubt, with each piece of evidence also subject to proof beyond a reasonable doubt—or human/biological diversity must be declared the result of a "design." In other words, leaving aside the unscientific basis of ID itself, it is not even using scientific reasoning in its evaluation of evolution.
My hostility is not to religious belief, but to inappropriate behavior and to intolerance. If ID proponents wish to teach their own children "the controversy" in the privacy of their own homes and churches, they're welcome to do so. They are not, however, welcome to bring their cryptozoological nonsense into a science classroom and impede my children's education. I don't need William Jennings Bryan in the classroom. Except, perhaps, the Sunday school classroom—and, indirectly, the American literature classroom—where he belongs.
Janus's famous mask had two faces, reflecting the two faces of drama: comedy and tragedy. ID proponents would have us believe that one of the faces of biological science is ID, which must be presented alongside (or at least in concert with) evolution so as to understand science as a whole. Leaving aside the irony of using images of polytheistic heathens to illuminate quasi-Christian fundamentalism, this actually clarifies the inquiry. Do we need "both faces" to understand science, scientific thought, and the scientific method? Clearly not; if this was true, then there would be corresponding "faces" in chemistry, in physics, in geology. ID is not one of the faces of science; it is at most a pimple, if only because nobody can possibly understand science or biology looking at (or wearing) a hypothetical mask of ID.