^^^^^ CB: He wouldn't be referring to people who were actually in their childhood. Rather to adults who were acting childish. That's why "infantile" seems more appropriate. To say it is a disease of childhood, is , in English, like saying he was criticizing some children who were Communists. Doesn't quite work well in English that way.
By the way, do you think there's an allusion to Freud ? ( somewhat tongue in cheek , maybe ).