A song is a commodity. If someone buys it and pays the appropriate reproduction fees it should be entirely up to them how they use it. There is no sense that it suggests the artist is supporting the cause or an individual who is playing it. It's just background music.
Think how bizarre it would be if I said that I don't want people using my book, say, to prop up the leg of a wonky table. Feel free to do so - buy as many as you like for this purpose. For that matter, provided you don't misquote me, and pay attention to copyright/copying fees etc., feel free to use text from my books as a backdrop to your events. Whatever they are. If I don't agree with you, that's fine. I'm not making the statement about your cause, any more than the manufacturer of the paint on the walls is.
Get a grip, music people. Deflate those egos a little.