Two of my best friends from childhood, my brother, and me all enlisted in the United States Marine Corps between 2000 and 2001. Our reasons were very similar to yours, though this was before 9/11 and (obviously) the Iraq war, so we didn't deal with that dynamic of it. My brother joined first, the pride of the organization appealed to him, and he wanted to force a personal transformation. Even though I'm older, I enlisted about a year later, because I was not doing well in school, and the few times I got to see him, he seemed confident and strong. I was nervous about boot camp, so I convinced one of the friends, who was also struggling in school, to join with me. The Marine corps has a buddy program where they will guarantee that you and a friend are put into the same platoon at boot camp. We both signed up for the DEP, immersed ourselves in Marine Corps culture, went running at 6:00 in the morning etc. etc. etc. My other childhood friend had moved to Ohio, and unbeknown to us, had also joined the Marine Corps.
I was the first one to get out: before I even shipped to boot camp, I dislocated my shoulder. I was terribly disappointed, and tried to convince the doctor to sign off on me anyway. He refused. When I told the recruiter, he flew into a rage, told me that I had no right to leave the program, that I was lying about my shoulder, and that he would get a doctor to certify my health. I called my brother, who told me that the DEP contract I had signed didn't mean anything, and that I had no obligations. I left the DEP, leaving my friend to go to boot camp by himself (something I've carried on my conscience). I had dropped out of school after joining the DEP, so I went back to live at home. I worked dead end jobs for 6 months before my parents told me that if I didn't do something productive they would start charging me rent. I was 21 and it looked like my life was going nowhere. I applied to a bunch of state schools that all rejected me, which scared the crap out of me, I finally enrolled at county college, and realizing that it was likely my last shot at school, earned my Associates with a 3.9 GPA. With my improved transcript I did finally get into state school, where I did nearly as well, and I finally ended up with a satisfying job in the financial industry.
My friend from Ohio was the second one to get out of the Marines. On August 3, 2005 he was riding in an amphibious assault vehicle in Haditha Iraq. He died along with the other 13 Marines in the vehicle from an IED attack. There were almost no remains to ship home. I attended the closed casket funeral, and to this day, facing his mother is the most difficult thing I've ever had to do. Both his parents were against the war from the beginning, and have since campaigned against it.
My brother was the third one to get out of the Marines. He received his discharge in September 2005, and immediately enrolled in College. He is on schedule to graduate this year. The difference in age and life experience between him and his classmates has alienated him to a degree, but he has performed very well. He has confided in my that he feels his 5 years in the USMC were a total waste. He feels very antagonistic toward the Marine Corps, and that feeling was shared by many of his Marine friends. The war in Iraq has enraged him, and he is a member of Iraq Veterans Against the War.
My friend that went to boot camp without me is still in the Marines. He has satisfied his service obligation, but recently volunteered to deploy to Iraq again (it will be his 4th deployment). He has mixed feelings about the War, generally opposes it, but feels a strong sense of duty to the other servicemen on the front lines. After going to boot camp, he enrolled in school again (he joined the reserves) and completely turned his academic performance around. He has told me that he is considering becoming an officer after he graduates. He blames himself for the death of our friend. As the person who talked him into joining, I will feel responsible if anything happens to him.
I guess my advice would be that this is a messy, tough decision. I won't give you my opinion, but to me the biggest concern is that the decision is essentially irreversible.