"Where Have All The Flowers Gone?" and "Turn, Turn, Turn!" and "If I Had a Hammer" are all Seeger works. How did I not know this? The documentary featured footage of him performing at Wolf Trap and I found some of the same stuff today on YouTube.
I now have the chorus to this old spiritual stuck in my head... which isn't exactly a bad thing. The words ring very true: "You've got to walk that lonesome valley. You've got to walk it by yourself. Nobody here can walk it for you. You've got to walk it by yourself."