Americans were horrified at the atrocities perpetrated by Hamas against Israeli villagers on October 7 this year. The brutality and futility of the attack rocked the imagination. Yet within days, we witnessed huge protest marches in U.S. and world capitals and universities in favor of Hamas. Their favored chant, “from the river to the sea,” means only one thing, and that is the annihilation of Israel and all its Jewish inhabitants. Such support for terrorism exploded in the 1970s as well in European cities and universities, and people wondered then about this same gleeful valorization of revolution by comfortable, privileged...