Why were people so horrible to each other in the 1800's?

People in 19th Century America during the 1800’s “Wild West” were so horrible to each other despite the fact that they had more or less modern comforts such as houses, grocery, agriculture, the ability to travel and communicate across distances and some medical technology available. Essentially, I’m asking why did people behave in a such ruthless and lawless fashion during this time?
Could you buy into the explanation that since they had just gotten through the Civil War many of them were left with PTSD (post traumatic stress syndrome) or other painful physical and mental scars which caused people to be generally dysfunctional during the “Wild West”? Perhaps they did not know how to cope with the social and emotional aftermath.