How could my son accept this as part of his life?

That's what he wants, and that's his life. As a parent, you should be there to support him with whatever he wants. Supporting him does not necessarily mean, for me, taking what's bad for him. Showing him why its bad is better. I guess, the question should be...How could the mother accept this as part of his son's life. He has committed to being a soldier, i think it's time you commit to supporting what he wants instead.