What is the theme in A Bright Shining Lie: John Paul Vann and America in Vietnam by Neil Sheehan?

Morality and choice make up a major theme in the book. A Bright Shining Lie deals with several situations where a person in the book must decide whether his intended actions are morally right or wrong. Vann had to chose several times, not only as a soldier, but also as a husband and father.