Part of the reason that quote from A Few Good Men is so powerful is that somewhere in the deep recesses of our mind, our fear finds that sentiment seductively comforting. Especially in post-9/11 America.
But truly, why do we defend human beings? Answer: because of their God-given dignity. We should not want defenders who would be willing to sacrifice their own God-given dignity in order to secure our lives. Some things are more precious than security. The dignity of the human person is certainly one of them.