If Gen. Augusto Pinochet ever stands trial in a Spanish court for crimes against humanity, the venue will be odd and ironic. That is because Spaniards, in the celebrated transition from the cruel dictatorship of Francisco Franco to democracy more than 20 years ago, never tried anyone for complicity in their villain’s crimes against humanity. Spain, in fact, never even created a truth commission to delve into the carnage of the Franco past. Instead, Spaniards abided by what they called el pacto del olvido (the pact of forgetting), an informal understanding that blame and revenge must be laid aside lest furies break loose and smash the movement toward democracy. Franco’s sins were hardly the lesser of Pinochet’s. In the wake of Franco’s 1939 victory in the Spanish Civil War, he and his henchmen killed thousands of their countrymen, often in summary executions or after swift and bogus trials. For the 36 years of his reign, he allowed no dissent; leftists languished in prisons for decades...