True but the world didn’t have a lot of sympathy for the Germans at that point. Unless there was something of value to them, I doubt the nazis would have done anything different.
It is interesting how war changed from WWI to WWII. My great grandfather came to the USA on the SS mount temple which was later sunk by the Germans in WWI. A couple of Mount Temple crew members were killed but they were firing back with deck mounted guns. The Germans removed the few remaing crew and passengers and scuttled the ship. Interestingly enough, the primary cargo was fossils.
Somewhere out there are photos of the sinking but I don’t feel like hunting them right now.
Most people think U-boats were designed to sink ships with torpedoes; they were actually designed to sink them with the deck gun (they couldn’t carry enough torpedoes to operate very effectively at any long range). Early in the war, the U-boats would surface next to the freighter, warn the captain (and let the crew abandon ship), then sink it with shells below the waterline.
As Britain fought back by arming freighters and using decoys (Q-ships) and escorts, the U-boats couldn’t risk surfacing like that (they were easy targets with thin hulls); the war became more brutal at that point.
There was one instance (possibly before the US was in the war) where people on a beach in Florida watched a U-boat sink a freighter; IIRC the U-boat was on the surface between the beach and the prey. Incredible.