Israel’s Knesset in July approved the first reading of a bill that would outlaw gay conversion therapy. Efforts to “reverse” homosexuality through psychology could soon be banned. Ultra-Orthodox coalition partners reacted furiously, triggering a crisis in the Netanyahu government.

The term “conversion,” which is on everyone’s lips these days, reminded me of a story from times long past, which actually doesn’t have much in common with the current events, but is still very interesting.

I was reminded of the Jewish visionary Theodor Herzl and his conversion plan for the Jewish people. Few people know that Herzl had an idea in 1893 that is actually quite difficult to swallow: He developed a plan for the mass conversion of Austrian Jews to Catholicism.

Herzl was so keen to find a solution for the Jewish people that he did not shy away from such radical ideas as the collective mass conversion of Jews to Christianity. For a time, he was convinced that total assimilation through conversion and intermarriage was the only...