I've been seeing stuff like that on the Net for many years. It is probably much worse in other discursive venues, like your neighborhood tavern. My rather constrained version of the argument for reparations evolved in just such an atmosphere; hence its smooth armor plate. Its one defect, I think, is that it requires the other side to be fairly strongly committed, rhetorically at least, to the nominal values of liberalism. The general population is not so committed and will rely on arguments from power, convention, and self-interest and will see little benefit to themselves in paying reparations. So you can win all the arguments and still get nowhere, practically speaking. The dumb stuff Horowitz and his friends put out is relatively easy to defeat; the great political inertia of the general public isn't. However, Horowitz's stirring of the issue may have some unintended benefits for the Left and we should be alert for opportunities. The first step toward destroying a reigning ideology is to destroy its belief in itself.