At some point the breaking takes on a life of its own and it is merely assumed that it will lead ineluctably to the glowing future. That is class warfare. Such classes can be ethnic - Jews and Tutsis, for two grim examples - economic, religious, or political.
It isn't that one cannot be politically progressive without descending into class warfare but nearly all of the worst abuses in the arena have come from progressivism. One is so accustomed to hearing the Nazis dismissed as "right-wing" that one sometimes forgets that they were politically progressive to a fault, that fault taking form in a few tens of millions of corpses. Hitler most certainly had a vision of a beautiful future world (assuming one were sufficiently Aryan). The devil turned out to be in the details.
This is, unfortunately, far from academic with respect to American politics. Where that imagined future involves equality of material possessions, some must lose a great deal so that others gain a little. "We're going to take things away from you for the common good." That "common good" is an illusory progressive future. The only real part is the taking.