Yeah, there is some of it, no doubt, but there are also people like Justin's in-law. I know that first hand, I used to work for them for several years.
People join the service for various reasons - just as they do with any other institution. Some of them need a crutch in their lives, other actually believe in this whole ideology. There are still others who look for venues to express their sadistic tendencies, but I understand that there tend to be weeded out (at least before Iraq) because they make poor soldiers. A good soldier acts on orders, not on his own sadistic impulses.
I also understand that the institution itself can have a rather negative influence on people in it, as the "institutional culture" tends to be very macho and very conservative. Some of it comes from above, no doubt, but a great deal comes from the rank and file. You need to remember that wimps who need a mental crutch in their lives will not show that they are wimps - they will hide behind macho appearances. Again, I've seen that a lot. At the same time, the Army was one of the first institutions in this country that eliminated racial segregation and curbed sexual harassment - when these were still seen as laughing stock in corporate America.
And one more thing - Army officers tend to have a much keener sense of reality than many spin doctors, politicos, pundits and academics - a definite plus in my book.
In sum, while am definitely not a big fan of the military - I would never join this institution and would do what I can to persuade people I know not to join it - I also think that simplistic caricatures of this institution are not very helpful to understand how it actually operates and what motivates people to join it.
Wojtek