AP Photo

As I surveyed the photographs of people in Cairo and elsewhere in the Arab world, mostly young and brimming with enthusiasm, often with fingers raised in a “V” for victory, I was reminded of three similar moments in recent Latin American history, each of which I witnessed firsthand: the Dominican revolution of 1965; the Sandinista revolution of 1979; and the inauguration of Jean-Bertrand Aristide as Haiti’s President in 1991.

Decades later, what looked at the time like promising divergences from an authoritarian, unjust, poverty-filled past is now, in essence, more of the same. Will the Arab...