LAST AUGUST a judge sentenced Brenton Tarrant, who murdered 51 people at two mosques in Christchurch, to life in prison with no possibility of parole. It was the first time a court in New Zealand had meted out such a sentence. Jacinda Ardern, the prime minister and a liberal icon, took grim satisfaction in the punishment. “Today I hope is the last where we have any cause to hear or utter the name of the terrorist,” she said. Lifelong imprisonment seems to be spreading as a punishment for the worst crimes. In 2019 Serbia passed “Tijana’s law” in response to the rape and murder of a 1...