I can't speak for all the people who joined the military, but for myself at least, hearing stories like Katya's are the reason I chose to put myself in harm's way. Hearing that lives were saved by men and women doing their duty inspired and humbled me, and hoping to emulate those folks played a big part in my own enlistment. Even though I can say that only a few lives were saved directly by my actions, every one is precious to me and makes me thankful that I was there.
I had many friends I grew up with who chose to serve, and sadly, not all of them made it back, but they all served with honor and dignity. Losing them will leave a hollow place in me, but they sacrificed themselves to protect those who couldn't fight, and if you gotta go, going out doing something noble is the way to do it.