Very interesting thread. As far as the Communism/Folk Song link is concerned it is useful to look at Charles Seeger (Pete's father) and Ruth Crawford Seeger (Michael, Peggy, and Barbara's mother - and Pete's step-mother). Both these two were leaders in the Modern Classical Music movements of the 19-teens and twenties specializing in dissonant counterpoint (about as far from folk music as you can get). When the Great Depression hit they were radicalized by the sight of the suffering citizens to the point that they actively and intentionally adopted folk music as the medium of best reaching the people (only after realizing that the stark modern music was not up to the task). Charles was part of a Communist group to produce and advance music that would help empower the people (or "turn them into communists" from some right-wing perspectives). He eventually found his way to the FDR New Deal bureaucracy promoting folk music esp. AMERICAN folk music and folklore. Eleanor R. was a supporter of the Seeger's work. Ruth Crawford Seeger (along with Alan and John Lomax) supplied the foundation for the folk movement of the 50's and 60's in that she transcribed and published several popular books of American folk songs which found there way into the U. S. schools. (My first exposure to folk music.)
And, of course, Pete carries this torch with his emphasis on the worldwide universality of the people's music. The thrill of my life was meeting Pete and being part of a session where he "taught" us how to lead groups in singing. (IMHO)We who love folk music owe a great debt to these dedicated people.