To understand that this is a part of the human condition whether we like it or not. That there are people, many people, in almost every society who like that way of life, who like inflicting pain or killing, who like to function in S-M relationships characterizing the military. Some may call it mental disorder, other - false consciousness, still other may chastise it with their blame games - but these reactions are mere expressions of impotence vis a vis this phenomenon. Yes, some of us are sadistic assholes and enjoy every bit of it, or better yet - there is a sadistic asshole in virtually everyone of us, waiting for the right set of circumstances to come out. The first step to understand it is to stop moral reproaching and blame games - that are nothing but meaningless babbling giving us a false sense of security in the face of what we do not understand and what threatens us.
BTW, if you think the Marines are hyper violent assholes, let me introduce you to Mr. Taylor, http://news.bbc.co.uk/2/hi/africa/2963086.stm a US-trained accused war criminal in Liberia whose followers' atrocities make the Marines look like schoolboys.
Wojtek