Reg Joe, I think you and HM are actually in agreement, witha slight miscommunication.
When the recruit volunteers, they are volunteering for whatever the military will subsequently require of them. (your point).
When the big wigs decide to invade somewhere, they do not go amongst the troops and say, "okay, who wants to volunteer for the invasion of Fubaristan?" The initial act of volunteering for the military is deemed to cover that already (HM's point) and if the powers decide to send you, they send you.
I believe this is not quite right, and that service-people can and do put themselves forward of additional tours if they feel up to it. This might count as "additional volunteering".
Is this right?
Anyway, back to the recent incident. What was the guy's supervising officer up to? His base commander? Medical staff? Even his buddies? Did no one notice any warning signs that he was losing it?
IMHO, that is where the responsibility lies.