“Given what you've said above, about the status of intelligent design as a scientific theory (i.e. that it has none), should we conclude that it therefore should be denied a voice within a science classroom?” Well, look at it this way. Do you want me to teach French in your chemistry class? What purpose would that serve? If a theory has no scientific evidence nor any hope of scientific evidence, then teaching it in a science class is not teaching science. Then, too, as I argued before, ID is inherently a religious theory, whether or not it employs explicitly religious terminology. So, besides being a waste of time, teaching ID as science runs afoul of the Constitution by imparting the cachet of science to a particular religious tenet.
As is my usual style, I'll address what I see as the minor points of contention before moving on the big ones. The minor point is this: there's a difference between (1) design theory necessarily entails the existence of at least one supernatural being and (2) design theory necessarily entails the existence of God as conceived by classical theism. ID is "inherently religious" only if (2) is true, not if (1) is true. I don't think I need to show that (2) is false; Kant did a perfectly good job of that in the Critique of Pure Reason in 1781. That's why design theorists assiduously avoid claiming that the supernatural designer is God -- it's because they know they can't get away with it -- not in an empirical or even political sense, but in a strictly philosophical sense. (To the extent that the "strictly philosophical" can be separated out from the empirical and the political!)
(In fact, I do believe that most people who support intelligent design are theists, and moreover, theists of a very specific sort. Their theism certainly feeds into their motives for wanting design theory to be true, and their motives for wanting it taught alongside evolutionary theory. But motives are not reasons, and the luminaries of the design revolution are all too keenly aware of that!)
The main point I want to address is this: "If a theory has no scientific evidence nor any hope of scientific evidence, then teaching it in a science class is not teaching science."
Whether or not I accept this depends on what is meant by "teaching science." If "teaching science" just means "conveying to students the best of contemporary scientific theories," then I'll concede the point without reservation. But here is where I demur. Instead, I want to broaden and deepen the meaning of "teaching science" to "teaching students how to evaluate scientific theories, how to appreciate the process whereby theories are generated and tested, and how to situate science in a cultural, historical, and political context."
I suppose I'm feeling somewhat frustrated both by the larger debate and by how this conversation is unfolding here on Impure Reason. What I'm interested doing is breaking down the artificial boundaries between the teaching of science, the teaching of history, the teaching of poetry. How can students appreciate Blake without appreciating Newton? How can they understand Romanticism without the Enlightenment? Or fundamentalism without understanding Biblical criticism and "Darwinism"? (Not to mention neo-Darwinism and the Modern Synthesis!)
What it comes down is this: why do we educate? If we educate so that the next crop of wage-slaves can take the place of those who have moved on, then fine -- but then, let's cut the bullshit about "democracy" and "citizenship." Or, let's put our money where our mouth is -- in which case, let's actually teach students how to think, how to listen, how to speak, how to reason, how to experience -- and if we do that, and if we seriously want to equip students with the cognitive tools they need to actually be the informed and responsible citizens we say we want them to be, then hell yes -- let's "teach the controversy" -- and bring some epistemology and philosophy of science and, why the hell not, some history and poetry into the science classroom too, and some science into the literature classroom.
Practical? Hell no! But worth doing? Hell yes!