I posted an excerpt from Korda's book on that subject. The planes were picking up downed fliers who could go right back into action against Britain. Dowding reasoned that, under the Geneva Convention, that made the planes fair game - red crosses or not. On the same grounds he felt that German fighter pilots would be justified in machine gunning British fliers parachuting from destroyed aircraft over England. Dowding followed the "rules of war" as he interpreted them.
The same could be said of Himmler.