"How could Pete or they have known about the atrocities of the Stalinist regime ? Who among us ordinary people could have sorted out the propaganda from the truth back in the 40s/50s ? Pete believed in the sharing of wealth, but he was living in a most capitalistic society and unable to change things to the way that socialism prefers."

Good point. In the era of the Popular Front, many people belonged to the CPUSA and later changed their minds when the found out the truth about Stalin. Some, vindictively, used this to persecute others or inform on people to be brought before HUAC, people like Burl Ives and Elia Kazan. Pete forgave them as most everyone bought into the "Uncle Joe" ruse.
Pete has apologized for his early support of Stalin many times, displaying a humility to be admired, not to be denigrated. Still, there are those who would smear Pete for his early mistakes because they have a political axe to grind, enjoying the defamation of a noble and productive character in the name of their self-righteous egotism and blind malevolence.