Well, as much of a jackhole as Kerry is, the full statement in context isn't all that ridiculous. He was talking specifically about a one-state solution -- Israel including all of the West Bank, etc. If that is the case, then the total Arab population would be close to the total Jewish population, and the voting-age Arab population likely would overtake that of Jews sometime in the next decade. So in that case, a democratic Israel likely could not remain a Jewish state, because Jews would be a minority.