I get your point but that was over 150 years ago. Life was a lot different back then. Life was short and brutal and people dixnt have 20th or 21st Century sensibilities or ideas of death. The Civil War marked some profound changes in warfare and it's not reasonable to think ordinary people could have anticipated that.
Some of our sensibilities are an evolution, which you would hope for. Evolution means progress, right? Improvement? It's a good thing. We would hope to be better.
Our ideas of death aren't necessarily an improvement but that's another issue. The point of looking back is to learn something, not to pass judgment on people out of their own time and out of their own context. Finger wagging serves no constructive purpose. The moving finger writes and having writ moves on. Nor all thy piety nor all thy wit shall lure it back to cancel half a line. Nor all thy tears wash out a word of it.
Yes people did picnic. Yes, they ran away in terror. Yes, that's hard for us to fathom.