I can answer the questions on mental health issues. I have to leave so I'll add more to this when I'm back home in a bit. It might be best to start by explaining that I'll be coming from this from a cultural perspective.

French philosopher Michel Foucault has a lot on the construct of madness. In Madness and Civilization, he divides insanity (i.e. mental illness) into three time periods. The Renaissance, the classical age and the modern age. The classical age made up the 17th and 18th centuries, so we can look at that. He believed that the mentally ill were dehumanised and should be confined/kept away from society because they presented a deviation from popular culture (Andrew Scull agrees with this). Mental illness at this point was not medicalised and people didn't really understand the consequences. Regardless of what you think of Foucault, it's important to realise that mental illness was not viewed as a medical problem (for the most part, obviously there were exceptions). So if a soldier were to have some sort of mental trauma, people would believe it was a break in his moral composition/character that would cause it.

Additionally, it's worth noting that there aren't any records that PTSD in its modern form actually existed prior to the late twentieth century. Edgar Jones has a really interesting paper on this. Psychological trauma, however, would have been overwhelmingly viewed as the fault of the individual. Memory and trauma can be read more about here.

To answer your question in the title, you might want to look at ideas of the deserving poor and the undeserving, too (I'll get sources when I'm back home).