These comments drew howls from gay-rights advocates, most of whom, we suspect, were objecting to the implication that homosexuality was comparable to practices like incest and bestiality, which most everyone still agrees are deviant. But Lithwick thinks the slippery-slope argument itself is fundamentally flawed: "The problem with the slippery slope argument is that it depends on inexact, and sometimes hysterical, comparisons," she writes. Also: "Slippery slopes are only metaphors. They are not intrinsic principles of law." Yet the way American constitutional law works, slippery slopes are almost inevitable--a point that is more easily understood if we think of same-sex marriage...