It has become a familiar political pas de deux. One side draws an analogy between some current policy or practice and 1930s Germany, as if Nazis provide the only measure of moral degradation. The other side uses outrage at the analogy as a shield to protect itself from having to justify that policy’s immorality in its own terms. And so it has been with the Gary Lineker controversy. A striking aspect of the debate over his tweet that the government’s “stop the boats” policy deploys “language that is not dissimilar to that used by Germany in the 30s” is that...