For some people, everything was wonderful before Lincoln and horrible afterwards.
The "Old Republic" certainly had its virtues, but it also had its weaknesses and its ugly side. I'm not attacking it, just saying that people shouldn't build up antebellum America to put later periods down.
In any event, if the Old Republic died, secession and the division of the country into two hostile blocs had a lot to do with it. After 1860 our history was going to be different, however things played out.
I was mainly interested in your word "unedenic," since neither my Websters' nor a google search produced a definition. The only reference to it I could find was something out of Tennessee Williams(!).
Then, slow witted as I am, I thought, well what about "edenic"? But "edenic" was also not there, however a shorter root, "Eden" was, and then slowly the light bulb comes on: Eden -> edenic -> unedenic. Oh, my...
OK...
If by "ugly side" you mean slavery, then of course. That problem was acknowledged by Thomas Jefferson in a draft of the Declaration of Independence, but was later removed to satisfy southerners.
It was again addressed with a compromise in the Constitution, and then with many other compromises before the Republican Revolution of 1860.
Jefferson and others had calculated how much it would cost the government just to buy up and free all the South's slaves. That number always seemed too astronomical, though turned out to be less than the cost in blood & treasure of the Civil War.
But I think Jefferson's exercise was pointless anyway, since the Old South was not going to give up her slaves without a fight, regardless.
It was a problem the "Old Republic" simply could not deal with, though I understand some have argued that in due time the Old South, on its own accord, would have abolished slavery. Somehow I doubt it.
So, how else was the "Old Republic" unedenic? No universal health care? No social security or unemployment insurance? Somehow I don't remember reading about those in "Old Eden." ;-)