Usually these propaganda comics were very clear with their messages. There was no question what they were talking about. In this one the point is rather obscure. Despite a lot of dialogue about how families are good and the Commies and fascists don't like 'em, the real message seems to be "be nice to your neighbor." A good message to be sure, but muddled by the way Harris dismisses the Palookas as "their kind" when the Palookas are white, middle-class people who look exactly like him and live in a house just like his. It'd make sense if the there was a religious, racial, or class difference between the two families, but Harris apparently bases his prejudice on the fact that Joe is the heavyweight champ. In the end the message is, "Don't prejudge the family of a sports star."
Link to the book:
Joe Palooka in It's All in the Family