It isn't a matter of "enjoying" killing people, as far as I can see. It is a matter of enjoying setting things right. Eliminating those people who brought so much misery to others. Do you really think that the men who liberated Aushwitz wouldn't have "enjoyed" killing those responsible? Of course they would. It doesn't mean that they are "killing machines", it means that they would be thrilled to have the opportunity to set things right.
Not as an attack on you personally, but it does appear that you subscribe to many of the same attitudes about the military that are so predominant in the mainstream media and on the left. Speaking now in generalities, not about you specifically, I see that no matter what a military member (or former military member) says about war, if it doesn't amount to a flat out statement of condemnation of warrior-like conduct, it is to be criticized, and viewed with abhorrence.
So, when warriors speak as such, while other warriors recognize exactly what they are saying, those who are critical of warriors and their profession most frequently take their words to have the worst possible meaning.
Personally, if I were a marine or soldier, I would probably find satisfaction in destroying the Taliban and other oppressive groups. That would include bringing worldly justice to those monsters.
The tank commanders and drivers in Iraq whoop and holler whenever they get the opportunity to drop a round downrange onto a sniper. It is what they do, and what they are. They are warriors. It doesn't mean that they take joy in the suffering and deaths of other people. It means they take satisfaction in doing exactly what they are supposed to do - break things and kill people - the right people, the monsters posing as humans, the Taliban, al Qaeda, terrorist of all stripes.