In an era in which society encourages each to do his own thing, and “right” is a relative term, a recent study seems to indicate many people do inherently have an understanding of morality at their core — and this may sometimes conflict with the actions required by military combat:

The conflicts that troops feel can range from survivor guilt from living through an attack where other troops died, to witnessing or participating in the unintentional killing of women or children, said researchers involved in the study.

The key quote comes near the end of the article:  Combat experienced US Marines were the subject group, and the study showed

Their condition [PTSD] was more closely linked to an inner conflict Read more