I thought "banned" implied songs that were in contention to be played on commercial radio, don't think a folk tune like that would have made it to radio back then. That song was from 1970, but a song from 1969 by MC5, "Kick out the jams" may be an earlier example of such language in a song. "Kick out the jams, mother****ers!".I'm not sure if this was banned completely but "Working Class Hero" by John Lennon was one of the first songs to have a word *beeped* out and hidden/not printed in the lyrics pages of the record...For the line;
"They hit you at home and they kick you at school, til you're so ****ing crazy you can't follow the rules"
Also in 1967 when the Rolling Stones had to perform on the Ed Sullivan show, they ridiculously had to change the lyrics to "Let's Spend the Night Together" to 'lets spend some time together'. I've only heard audio of it, but I've read that during the performance Jagger was rolling his eyes as he sung the chorus, can't blame him either.