Grief is necessary. Pain, longing and loss are what give people depth. Without them we are superficial beings seeking only self-gratification. With them we reach outside of ourselves to touch the life of another. The cybermen are not monsters for encasing themselves in metal shells but because in the process they chose not to feel pain. They did not understand the way in which joy and sorrow are intertwined. Danny may not have become the gentle and compassionate being he is without the horror of war. Its easy to be glib before one experiences loss. You can willfully refuse to acknowledge the fact but there is no denying that pain changes us and often for the better. Danny is a hero because he takes that pain and uses it to become something greater than what he was.