Saving civilians is incumbent on you in war whenever possible. Not like North Vietnam is going to start doing some strafing runs on your fleet either for an excuse.
You think only two countries would destroy a few helicopters' worth of value to rescue allied civilians during wartime evacuations where they're not under fire? I suspect we'd be pushing a catalogue of 100+ countries. Loads of examples from WW2 like Dunkirk/Operation Hannibal where you see the sacrifice of material for civilians.
No, there were dozens of examples during that North Atlantic campaign.
The U-boats would presumably have continued to rescue enemy military and civilian survivors throughout the war, if it hadn't been for the war crimes of the USAF which bombed the rescuers.
Saving civilians is incumbent on you in war whenever possible. Not like North Vietnam is going to start doing some strafing runs on your fleet either for an excuse.