war and being able to kill

The Biggest Star Wars Plot Hole, Explained By Science

In regards to the dehumanization aspect of storm-trooper gear, I remember that when I first saw Star Wars as a child, it never occurred to me that storm-troopers were supposed to be humans in armor, even in spite of seeing Luke and Han putting on the gear. To me, stormtroopers were some kind of robot/monster. Even when I was introduced to the idea of there being real *people* inside those things, it did not compute... I could understand that to make the movies, there had to be people wearing costumes pretending to be stormtroopers, but I couldn't believe that in the actual story, they were supposed to be human, too. Even when I got a bit older, the subject was still murky for me, because I had heard that stormtroopers were clones, and it seemed that if clones were stormtroopers, they couldn't be regular people.

These are interesting articles linked from the one above, regarding human reluctance to kill:

Hope on the Battlefield

Hidden Wounds