The funniest part in all this is that the actual Scots-Irish underclass of the South generally hated the upper classes of plantation owners that spearheaded the Confederacy. Most Scots-Irish soldiers in the Confederacy were conscripts or only joined the Confederate Army in the beginning of the war because they didn't want federal troops in their own backyards.
Appalachia, the region with the highest concentration of Scots-Irish in the entire country back then and even to this day, was a hotbed of pro-Union sentiment. They may not have cared for black slaves but they hated the planters too.
For fuck's sake, West Virginia became a state purely due to the fact all those Scots-Irish mountaineers hated the Confederate ruling class and saw the Union as the lesser of two evils.
There were also pro-Union militias in territories that were nominal Confederate areas that were comprised of Scots-Irish hillbillies and the reason why Kentucky was a neutral border state instead of just joining the Confederacy is because of both the proximity to Ohio and the Scots-Irish hillbillies in the mountains of Eastern Kentucky who were too poor to own slaves and couldn't compete in the old plantation economy.
My Scots-Irish ancestors fought in the Civil War for the North, even if they personally didn't like the black slaves on the plantations.
The idea of the Scots-Irish underclass being staunch supporters of slavery and valorously giving their lives to the Southern cause is a revisionist myth that emerged many decades after the war ended.
The majority of the plantation and middle classes of the South that did support the Confederacy were Anglos of pure English stock and Episcopalian upbringing who viewed the largely Calvinist Scots-Irish with contempt and saw them as backwards barbarian hicks.
The other portions of the plantation classes that weren't Anglo were either French Creoles in Louisiana or Sephardic Jews in Missisippi and South Carolina.