[From a colleague:] The way a scientific theory gets empirically established is not by showing that the evidence requires that precise theory. That is an impossible task–there are always infinitely many theories that fit the data. Rather, it gets established through showing that the evidence discredits the main alternative theories but does not discredit this theory.
The same is true for evolution. (In fact, it was in the context of evolution that I first met this idea.) Darwin established his theory through arguing that there was evidence that discredited the main alternative theory, namely creationism, but that did not discredit his theory.
If this is correct, then in order to teach students that neo-Darwinian evolution is true (as you see, this is an ad hominem formulation) other than merely by an argument from authority, one needs to show them the evidence for evolution. But the evidence for a theory is not so much evidence for a theory as evidence that discredits the main alternate theories. (If the evidence doesn’t discredit alternate theories, then the theory that it “supports” is vacuous with respect to the evidence.) In Darwin’s time, creationism was the main alternate theory. In our time, in addition to creationism, there is ID.
Thus, to establish neo-Darwinian evolution, one must either teach creationism or ID, and show how it is (allegedly) discredited by the evidence. A failure to do that is a failure to present the evidence for neo-Darwinism. And to avoid strawmanning, the better of the two theories, creationism or ID, or else both, should be presented.
Now, if neither creationism nor ID is science, then evolution is unique among scientific theories. Other scientific theories are established by arguing against scientific alternatives. But if creationism and ID are not science, then evolution is established by arguing against non-scientific alternatives. If one has a bias against non-scientific theories, then one should see this as an unfortunate fact, one that impairs the epistemic justification of evolution, since evolution has not had the chance to fight it out against any well worked-out scientific theory. (Lamarckianism may be an exception, but the details have not been sufficiently worked out. The same objection can be levied against ID.)
The reason for this is that, as far as I know, evolution is the only theory in the canon of science which is established primarily through methodological naturalism, in the precise sense that the central arguments for it are of the form: “This is the only possible explanation consistent with MN.” This weakens the evidential force of evolution.