Prominent philosopher and legal scholar Thomas Nagel, an atheist, endorses an argument that is obvious: if the argument against intelligent design in biology (Darwinism) counts as a scientific argument, then the argument for intelligent design in biology must count as a scientific argument, because the two differing conclusions are just the negative and affirmative denouement of the same argument. That is of course not to say that one or the other argument about design is true; it is merely to say the obvious: that for either to be true, the question of intelligent design must be a scientific question.
Nagel applies this self-evident observation to the teaching of evolution in schools:
From the beginning it has been commonplace to present the theory of evolution by random mutation and natural selection as an alternative to intentional design as an explanation of the functional organization of living organisms. The evidence for the theory is supposed to be evidence for the absence of purpose in the causation of the development of life-forms on this planet. It is not just the theory that life evolved over billions of years, and that all species are descended from a common ancestor. Its deﬁning element is the claim that all this happened as the result of the appearance of random and purposeless mutations in the genetic material followed by natural selection due to the resulting heritable variations in reproductive ﬁtness. It displaces design by proposing an alternative...It is therefore puzzling that the denial of this inference, i.e., the claim that the evidence offered for the theory does not support the kind of explanation it proposes, and that the purposive alternative has not been displaced, should be dismissed as not science. The contention seems to be that, although science can demonstrate the falsehood of the design hypothesis, no evidence against that demonstration can be regarded as scientiﬁc support for the hypothesis. Only the falsehood, and not the truth, of ID can count as a scientiﬁc claim.
But what does any of this matter when they have the decisive counter-argument of shrieking "Creationist!" like scared little schoolgirls? As far as I've been able to gather the last few years, that's all they have left.