In his Redeeming the Enlightenment: Christianity and the Liberal Virtues (Radical Traditions), Bruce Ward examines the paradoxes of the peculiarly modern virtue of tolerance (113-7).
If tolerance is understood as forbearance toward what is morally repugnant, it is not morally indifferent or neutral but is morally founded. Endurance of the intolerable can be a virtue, but it’s a question whether it’s a virtue that can fly in our age of moral relativism. Tolerance in this sense is subverted not supported by relativism.
If tolerance is understood as indifference toward difference, it will wither away over time. If everything is truly indifferent, then tolerance becomes unnecessary. Apathy will be sufficient.
If tolerance is celebration of difference, then it clashes with some of the other desiderata of modern culture. Celebration of difference, Ward points out, must include celebration of the groups that transmit that diversity. What if the group is hostile to toleration? Should its intolerance be celebrated? What if the group imposes an orthodoxy on its members? Should the limit of individual freedom be celebrated?
Ward quotes Allan Levine (Early Modern Skepticism and the Origins of Toleration): “The problem is that while toleration has never been more widely applied than in the western world today, the . . . grounds upon which it has been defended are becoming difficult to justify philosophically.”