I'm not so sure. Collectivism, i.e. communism, requires the subordination of the individual to the state in exchange for the putative promise of the greatest good for the greatest number of people. Most people, however, would rather not give up their individuality so the communist state must force them do so, beginning with persuasion via propaganda, followed by imprisonment and finally, if that fails, liquidation. Since communism cannot work unless all go along with the gag, Stalin can hardly be considered guilty of excess, merely the prosecution of Marxist-Leninist ideology with vigorous and, you might say, religious fervor. Mao and Pol Pot did exactly the same in later years.
For Seeger to denounce Stalin without denouncing communism is disingenuous. If he still believes in it he ought to recognize in order for it to obtain, the brutal methods used by Stalin have to be used, just as they are today in North Korea and Cuba. If he and others like-minded think one hundred percent literacy and universal (if mediocre--how many desperately ill people fly to those two countries for advanced treatments unavailable in the U.S.?) health care are worth the brutality necessary to bring it about, they ought come right out and say so. At the same time, they might also admit their belief in the singularly non-Catholic (but paradigmatically liberal Protestant) notion the perfectibility of man and its corollary, the possibility of heaven on earth, while acknowledging those goals may only be attainable by the liquidation of every last one of us.