Over at the Volokh Conspiracy, Ilya Somin and Eugene Volokh have a couple of posts on the claim by some that the Air Force is unconstitutional under originalism. Of course, this is silly. The Army and Navy are not limited by the actual or the type of weapons that were employed in 1789. There is no reason to believe that the terms "Army" or "Navy" would have been understood this way. Just as new technologies such as balloons and canons would have been easily assimilated into the Army without a second thought about whether they were really part of the Army, so could airplanes and jets.
Ilya lists several prominent law professors who accept this criticism of originalism. The question is why they accept this argument. One reason seems straightforward. Sadly, it turns out that critics of originalism tend not to be good at practicing originalism. I have often heard this comment made by other originalist scholars. So, for example, when one reviews an article making both originalist and normative claims about a matter, by an author who does not believe in originalism, it is not surprising when the originalist claim turns out to be quite weak.
Originalism is hard to do -- It only seems easy. Thus, people who do not practice it regularly are prone to making mistakes. But another reason also, it would seem, contributes here. A critic of originalism would be quick to accept silly results produced by originalism. "Hey, look here, look at this absurd result created by this ridiculous method." Thus, it is the motivations combined with the difficulty that appears to be the source of the problem.
Of course, originalist errors are not confined to critics of originalism. Advocates of originalism often make a similar error: they interpret the original meaning too favorably in terms of modern sensibilities. For example, in my view, the First Amendment Free Speech provision is far less attractive than many originalists seem to assume. The unconstitutionality of the Sedition Act was at best a hard case. But the errors produced by advocates of originalism are less egregious because they are often practitioners of originalism and therefore have more knowledge of how the method is practiced. Moreover, they have an incentive to practice it in a manner that has integrity.