This is one of the most beautiful scenes in all of Star Trek. Horrible, but this has always been necessary. At some point, someone has to give an order like this. And in an individual's career, I hope that it doesn't occur, but they absolutely must be prepared to.The final test in the Bridge officers exam that Dee took on screen, that we all saw, required that Deanna save the ship by ordering one of her crewmen to sacrifice themselves for the good of the many. I don't suppose it's always Geordie that has to be murdered, every time anyone takes this exam on any ship ship in the fleet, but what if it were?
In the movie 'Gettysburg' I think that there is a line 'that to be a good soldier, one has has to love the Army beyond almost anything else, but to be a good officer, one has to be willing to destroy that which you love the most.'
Or if you perfer, firefighters, they have to go into the fire, taking appropriate precautions to rescue...knowing that they might succeed, but not come out...
This is why you should love firefighters, because they are willing to die for you., a stranger.
This is the essence...of being many things.