I watched most of the movie Paradise Road yesterday. I recommend it, by the way. It's about a large group of women who were captured in Singapore during World War II and taken prisoner by the Japanese government to the island of Sumatra. It's quite moving.
The lead character, Adrienne Pargiter, played by Glenn Close, puts an orchestra together to sing Dvorak's New World Symphony a capella. It's amazingly good. I had never heard Dvorak's symphony done a capella before first seeing this movie. The Japanese prison guards are moved by it and, momentarily, become slightly less inhumane.
Later, one of the guards asks Pargiter if she will put together an arrangement of a Japanese folk song. She refuses and it's clear, from her tone and body language, that this is an issue of principle for her. She hates what they have done to the women so much that she refuses to cooperate.
It seems clear from the context that some of the guards and even the prison commander are willing to trade. The Japanese soldiers have, apparently, stolen their rations, withheld quinine, and generally been nasty. But earlier in the movie a Jewish doctor in the camp, Dr. Verstak (played by Francis McDormand) managed to get quinine by trading or making concessions. (I've forgotten which.)
So in refusing to conduct the Japanese song, Pargiter is giving up a chance to trade for food and/or quinine, which could save innocent people's lives.
I don't see this as a question of principle. Remember, they had been asked to sing a folk song, not the Japanese anthem. (Even with the Japanese anthem, I would have agreed if it had got food or quinine for some of the prisoners.)
I believe in living by strong principles. But I also believe that you should identify very clearly where there really is a principle at stake and where there isn't.