When a military person stands, we all clap. Even those who are pacifist will clap because they recognize the sacrificial service - even if the person is actually against war all together.
We applaud those who serve our world and nation in ways that are "above and beyond". We would want our children to be willing to work in the world for causes that transcend the individual. Values such as service, freedom, selflessness, justice and hope are values that we all can affirm. Which is why we clap when the military stands up.
I wonder why we do not have the same sense of applause when someone in the Peace Corps stands up?