My son is 20, in his 2nd year in college, contracted with the Army ROTC, but will likely get out of that contract since he was offered a slot in the U.S. Coast Guard Academy and is waiting to hear from the Naval Academy. My father was a chaplain in the Army during the Vietnam era and buried a few hundred soldiers. My wife's dad was a pilot in WWII and a flight instructor during Korea and was one of the first planes in to rescue survivors from the Bataan march and prison camp (people died on his plane as he was flying them back care and treatment) I am scared to death my son will get killed or maimed and worry a great deal about what could happen to him in any of these branches of service. But I am VERY proud that he wants to serve this country, not just his own interests (or his parent's) and that he finds the well being our nation and freedoms to be more important than his own and worth the risk incurred in defending those freedoms. My son's grandfathers told him about the horrors of war, but also explained how freedom wasn't free, but came at a high cost sometimes.
In every good parent's life there comes a time when it is time to "Let go and let God" - I don't know your religious beliefs, but I trust that God's will is going to be done no matter what I do, so I have just handed it over to him and asked my son to just always seek to do what that "still small voice" inside him tells him is the right thing. It is the job of a parent to "train a child up in the way that he should go," but once you've raised that child, you MUST let go of that child and let him/her enter the world and face it on their own terms. Make sure you child knows you love him and that you will always be there for him, but as he enters the adult world, he needs your support and cheer-leading as well, not your hand holding and fearful running of interference for him.
Your concerns are those to some degree or another of every parent with a child in the military, but the odds of what you fear taking place are low. You hear about people who snap, get maimed, blown up, have serious PTSD issues because they are NOT the norm. The media pumps those stories up and they take on a life of their own, but they are NOT normal. What normally happens is BORING. No one reads articles about the guy who went into the army did a tour in Afghanistan, came home, married, had 2.5 kids and works at the local bank as a loan officer - but that's my 2nd cousin, 2 tours of Iraq, 1 in Afghanistan, 25 years in the army, worked up from grunt to Captain, retired and now works as an analyst at a bank. Never killed anyone, never got shot at (and his job was ordinance collection and disposal - rounding up AK-47's and weapons caches and destroying them). No one ever heard of him because it is not exciting or interesting. The abnormal is the norm for media reporting. The normal is typically ignored since it happens every day. Consider the fact that at least some of your fears are fueled by a sensationalist media and are not remotely connected to what usually takes place.
Don't give into your fears, it's OK to have them, but celebrate your son, let him know you love and support him no matter what decision he makes and understand it is HIS decision, he just wants YOUR support whatever he decides.