The scenes at Sydney’s Opera House on October 9, catapulted around the world, tarnished Australia’s international reputation as a multicultural success story.

I remember that night vividly. I was at home, complying with the NSW Police warning to Jews to stay home for our safety. Not every Jewish Sydneysider was as compliant, and the Australian Jewish Association (AJA) was receiving a stream of escalating footage of an enraged crowd burning an Israeli flag, lighting flares, and chanting antisemitic chants, all while police watched on.

It’s noteworthy that the crowd had gathered barely 48 hours after the largest massacre of Jews since the...