Significant life events, good bad or otherwise, are bound to have lasting influences on people. I think I'd be more concerned about someone who experienced a traumatic event and wasn't affected by it than I would be over a person who did become affected. Traumatic events are traumatic, and that's just life.
Seems rather obvious that if you drug someone into a state of chemical happiness, they aren't going to exhibit any of their former fear or anxiety. But at some point you have to wonder if drugging away the person's normal and natural responses doesn't amount to drugging away some of the person. Is it worth it?
(Yeah, it probably is worth it. I don't want soldiers to have to suffer needlessly for the rest of their lives. But at some point don't you have to accept that going to war is a life experience like any other, one that will have an influence on the people involved?)