As I understand it, sailors have strong ethics because the sea is the common enemy of all. Even sailors on ships at war will rescue the enemy after incapacitating their boat.
Yeah, but if you're a ship with a skeleton crew of civilians, you're going to think twice about rescuing a full compliment of soldiers from a dictatorship that just tried to sink you with no reason whatsoever.
There can not be any thinking twice about pulling people from the water. Even Somali pirates were first pulled up from their junks, and only then the boats were used for target practice.
EDIT: and they, being pirates, were subject to being killed on the spot.
IIRC uboats were only “supposed” to sink ships if they could aid in rescuing the crew and passengers after... but gave that policy up when the Allies kept attacking them with aircraft while they were conducting rescue operations.