President-elect Trump’s choice for ambassador to Israel, the attorney David Friedman, has been received in some quarters with contempt and disbelief. Mr. Friedman’s presumed failings are said to be many. As a lawyer, he has no diplomatic or foreign policy experience. He is a right-wing “extremist,” supposedly because he supports expanding settlements and moving the U.S. embassy from Tel Aviv to Jerusalem.

At its core, criticism of Mr. Friedman reflects the erroneous notion that only professionally trained diplomats can do...