How was Arlo Guthrie's song "Alice's Restaurant" a commentary on the draft?

It is a straight-faced sarcastic protest against the Vietnam War draft. It is based on a true story from Arlo Guthrie's life where he was prevented from being drafted because of his arrest record for littering. The song led up to him advising the future draft dodgers to go into the draft office singing the chorus of his song to prove themselves unfit for military service.