Really tough.Ok.
How about coming up with a list of songs you really DO care about that you really WANT to sing. Then get creative. Figure out how they can be seen as protest songs. The idea is not to try to fool anyone but to look at the songs from a different angle.
A song doesn't have to be about the Viet Nam war or unionization to be a protest song. Think of "Hard is the fortune of all womankind." No matter what a woman's age or race or home town that's got to ring a bell. "How can a poor man live in times like these" will probably be relevant forever.
Any song that offers a vision of how the world could be a better place is as much a protest song as a song that complains about the world as it is.