The man or character in Vonnegut's novel spouting off Marxist-styled class-warfare rhetoric is hardly some moral/ethical person himself considering he's a traitor, a sellout, and bearing his soul and justifying his decisions to do so to a cause, regime, that did unspeakable, horrendous things to Jews, homosexuals, Gypsies, Soviet, Allied POWs, ordinary German political dissidents who were taken into "protective custody", Poles, Czechs, anyone who opposed or spoke out against Nazis grand Volkstaat, or VolksGemenieShaat, " people's ethnic community" or opposed the concentration camps, overcrowded, squalid disease-riden Polish ghettos, or the death camps laid out in perfect, meticulous, bureaucratic order and planning after the Wannasee Conference.
If he was going to truly sellout or betray his country with those kinds of sentiments, it would made a lot more sense to defect to the Soviet Union before and after WWII.