I'd say the reasons are almost as varied as those who choose to serve, and also for those who make it a career.

Both Swofford's and Bowden books are great books for insight into the military mind, but there are a lot more, and while a lot of the opinions and sentiments will vary dependsing on the authors period of service, as well as his or her experiences, you may find some common themes.

Good post.

This is SGT Louis Quinones from the 101st Airborne Division heading to Iraq in sep 2005. Trying to get an email address or contact for Anthony Swofford. I was a marine from 87-91 and just loved his book. I was a pog in the marines but now a combat soldier and see so much differences from the army and the marine corps (their are similarities as well). So if anybody has a contact email, please email me. Hooah and/or Ooh-Rah

Jarhead is indeed a great read, but I think Swofford's various morality lectures and dubious political statements, particularly toward the end of the book, are a bit gratuitous.
Of course he's entitled to his own opinions about the validity and necessissity of the '91 gulf war, but I don't think that his award-winning author status gives him license to claim to speak for all, or even most, of his fellow returning combat vets.
It would have been nice if he'd admitted this somewhere in the book, but rather, he comes across to me as someone who's claimed the moral high ground and looks down with disgust on everyone who disagrees with him, and for that reason, I think a lot of vets feel betrayed.