It's less surprising when you click through and realize that it's by David Frum, who has had a number of sensible things to say about immigration, starting with a positive review of Alien Nation twenty years ago.(Jacket blurb: “Don’t be misled by the verbal pyrotechnics: Brimelow presents his case with a prosecutor’s thoroughness. … No reformer can avoid grappling with the formidable work of Peter Brimelow.”)
But of course, the answer to why no one in public life is saying it is because all criticism of immigrants it taboo, as a result of multicultural solidarity on the left...and neoconservative enforcement on the right.
That is, various "conservatives", including especially David Frum, have attacked any conservative who spoke about immigration in the wrong way.
While it's supposed to a critique of paleocon anti-imperialism, immigration comes up seven times in a Control-F search, one of which is this admission: "It’s odd: 9/11 actually vindicated some of the things that the paleos had been arguing, particularly about immigration and national cohesion."
Also mentioned in the piece: paleocon opposition to "civil rights", criticism of MLK, a quote from a 1994 speech by Sam Francis to the effect that “The civilization that we as whites created in Europe and America could not have developed apart from the genetic endowments of the creating people", and, of course, defense of "the Southern Confederacy of the 1860s."
So with all that, associated with the accusation of virtual treason, you can see why Conservatism, Inc. writers would be afraid to touch the subject.