I can't say I've ever killed anyone. I've fantasied about it a few times (I think everyone does occasionally about /that/ person in their life), but from what I've read on the subject, and from first hand accounts from military personnel etc, there are two types of people:
The first, and more common is to question it. Hesitate. Maybe you pull the trigger, maybe you just can't. Either way, it won't be pleasant for you. Some people manage to get over it. Some drink themselves into a stupor, sometimes to death. These are the people who's purpose lays back in base camp, not out warring with other tribes. There is no shame in this; we need both types of people in society but some just aren't cut that way. A friend of mine told me a story about his sniper training. They would look down sights at a target brushing their teeth or whatever, and 75% to 90% of the recruits couldn't pull the trigger. They would say things like "What? Shoot him? Now? In the back?" Most just couldn't do it unless their life was in immediate danger; in which case no one /chooses/ to kill, instinct and reflexes take over. Their body pulls the trigger for them out of self-preservation.
The second type of person is the person who always CAN pull the trigger. They don't /wan't/ to per se, but they will feel no remorse if they have to or if they are ordered to. Regardless if their life is in immediate danger or not, they can kill if they choose to. Ever watch an action movie where a character compares it to "taking out the trash"? They are this category. These are nature's warriors. The ones you send out on the front lines with a spear to keep the rest of us safe. The aforementioned sniper says <10% of recruits fall into the group.
Either way, it won't be enjoyable. At best, you won't feel anything, at worst you will spiral into suicidal depression.
There is technically a third group who enjoys it, but these people are incredibly rare and fall under the category of psychopaths; people who shoot up schools or clubs just because they can. Because they think the world owes them something. Because they are looking for the next high. Whatever. Either way, in the final analysis they are wholly evil and broken, and don't last long before the justice system catches them or they kill themselves.
