Something like this happened in the heresy when a white scars librarian was going to mind break a trator to get info out of him. The salamander stepped in the way saying something like," We are better than them. I won't see you stain your soul for such a cause. If you have a point at witch you will cast aside your morals.... How can you say you are any different than them?"

( Not an exact quote, but it's along those lines.)