Well, I haven't seen your workshops, and I don't know what ages the students are, but some thoughts do come to mind. The idea of getting on trouble for being honest, for one. You could tell them about Victor Jara's execution in front of a football stadium full of witnesses by having his hands cut off so that he couldn't play guitar any more, and his response by singing for those last minutes he had to live.
For non-lethal results, you could use Pete Seeger, both the environmental (Sloop Clearwater) and political (McCarthy hearings) aspects.
I'd see what I could steal, er, learn from Grit Laskin, James Keelahan, Si Khan, and Utah Phillips. I'd ask the kids to turn you on to songs from their chosen genres.
If there are problems with kids wearing "gang colors", you could show how that old St. Pat's chestnut, is about people being killed by the government for wearing green.
Just some random thoughts, I hope they help.