The modern age is clogged with—or more descriptively, cursed by—political causes. Every such cause trumpets peaceful and progressive virtues but, in practice, each is a turbulence of violence. The worst of them—Communism, Nazism, Islamism—provide the ideological framework for mass murder. With whatever messianic fervor a political cause is promoted, at its core is the defense of some partisan interest, usually religious or national. Purportedly universal causes—pacifism, human rights, ecological issues—have a similar tendency to define themselves as moral absolutes that legitimize aggression. And as that old rake Norman Douglas was the first to point out, somebody will be found to defend even the vilest cause. An English poet, for instance, judged the Khmer Rouge to be merciful because in spite of their poverty they shot their victims rather than clubbing them to death.

A cause offers purpose where p ...