I sat this week with Hussein Agha, a man who has given his working life to seeking peace between Israelis and Palestinians, negotiating from the Palestinian side of the table. He was gloomier than I have ever seen him, adamant that peace between the two sides can never, ever come. Because, Agha explained, this conflict was not about mere lines on a map or forms of words, the goods in which diplomats trade. This was about emotions, and specifically hatreds. Hatreds that, he feared, are becoming too murderous to contain. “It’s biblical,” he said. What he had in mind was...