TANC, this morning on KFOG they had Wavy Gravy in the studio stumping for the upcoming benefit for his Sava Foundation, which will have Crosby/Nash headlining, and Graham Nash called in to chat also.
Nash said that he is always there whenever Wavy calls him for something, and then told the story of the one exception. In 1969 Wavy called Nash to ask him to get the guys together to do a benefit to help raise money for the defense fund of the Chicago 7. Nash said that he and Crosby were available, but Stills & Young weren't, so instead he wrote the song "Chicago".
ETA: the lyrics read like a mea culpa now that I heard the story.
Though your brother's bound and gagged
And they've chained him to a chair
Won't you please come to Chicago
Just to sing?