His depiction of violence is just realism. I don't see the need to subscribe symbolic value to it. Texas/Mexico (the distinction was blurry then) in the 1800s was a really dangerous place, with a lot of competing factions centered in a small area. All the history of the time that I've ever read indicates McCarthy's violent scenes are by no means beyond normal.

Very true, and while the 1800's were a violent time I think that McCarthy writes about violence as if its a part of our makeup. I think i mentioned it in an earlier post but at the very start of the book he added 3 epigrams:

Your ideas are terrifying and your hearts are faint. Your acts of pity and cruelty are absurd, committed with no calm, as if they were irresistible. Finally, you fear blood more and more. Blood and time–Paul Valery

It is not to be thought that the life of darkness is sunk in misery and lost as if in sorrow. There is no sorrowing. For sorrow is a thing that is swallowed up in death, and death and dying are the very life of the darkness–Jacob Boehme

Clark, who led last year’s expedition to the Afar region of northern Ethiopia, and UC Berkeley colleague Tim D. White, also said that a reexamination of a 300,000-year-old fossil skull found in the same region earlier shows evidence of having been scalped–The Yuma Daily Sun, June 13, 1982

It's not that this one period is violent; its that we as species are violent and always have been. So in a sense perhaps the violence in this novel should not be considered all that important to what the author is trying to say.