On a hill called Champel outside Geneva in 1553, green oak branches crackled in flames round the feet of a 42-year-old Spanish heretic named Michael Servetus. His heresy: that God was not Three-in-One but One, that man was not innately sinful but innately good. Throughout a three-months' trial he had fought hard and long against stern John Calvin, "the Protestant Pope of Geneva," and had lost. But in sending Servetus to the stake, Calvin's Council gave the tiny, free-thinking sect, now known as Unitarians, its founder-martyr.
This week the ultraliberal, highbrow Unitarians...