Bob,
It is our belief system, our "we are in this situation together and I will do what I can to save my brothers" type of attitude and beliefs that cause us to do the impossible or the incomprehensable. Whether we volunteered to do what we were doing or were drafted to do it made no difference at that point, we were there and our training, beliefs, and what we had all gone through up to that point in the conflict that instilled the fight in the man. Think about it a little, we all talked war because we were in one, we all had the same attitude because talked with our brothers, we all looked at other American soldiers as our brothers because we were all in a similar mess. We believed what we heard from our brothers, and our attitudes melded and solidified. We were fighting the same enemy, and we categorized him with the same perjoritives that instilled the same distrust and hatred in all of us. Fighting back to back, and killing to defend our brothers became a normal situation due to the amount of time that we had spent in that situation. The newbies didn't have it, so we didn't readily accept them, as they remained with us for longer periods of time, they became us, which made them like us, and therefore brothers.

We were forced into a psychological mess and our brains adapted and became alike in order to survive. Those changes to the brain were not changes made easily, they were driven into our brain through shock and violence that is unparalleled in the protected free world that we live in today. Those changes made permanent changes to core of our brains, and today we react differently to simple situations than do our fellow men who have never seen combat. That is why we have the attitude of brothers who say "If you weren't there, you don't know what I am talking about".

We aren't strange people, but we all have the same habits that were driven into us by that situation. Who among us isn't a perfectionist? Who among us isn't or hasn't been a work-a-holic, one who works extra hard for acceptance and to insure that what we do is better than what others who haven't been there do? Who among us doesn't flock to others who have similar feelings about our friends that we consider brothers, and of those same people would rather be left alone than to have to deal with the dummies who haven't had our experiences. We are isolationists who seek friendship, but the friendships that we seek are limited or conditional except for those of people with similar backgrounds.

Who are we, and why do we do what we do, is a question that can best be answered by experience.