Well, I wasn't there, so FAIK you may be right.
What I was taught in college was that the ante-bellum South was more tolerant of Catholics than the ante-bellum North; and (without getting into whether there was a cause-effect relationship or which way it ran if so) a higher fraction of Southrons than Yankees were Catholic.
IME on "your" side is the fact that I never learned the family history of any Southron Catholic family that had been that before The War.
My parents and grandparents were Methodists -- the quiet kind. Their parents and grandparents were also Methodists -- not
the quite kind, but rather the "shouting" kind.
During my life in the South, Baptist denominations were quite ubiquitous and influential (or, at least, were credited -- sometimes pejoratively -- with influence).
OTOH on "my" side is the famous "Rum, Romanism, and Rebellion" remark of some post-Reconstruction Yankee (radical?) Republican politician.
In the final week of the campaign, the Blaine campaign suffered a catastrophe. At a Republican meeting attended by Blaine, a group of New York preachers castigated the Mugwumps. Their spokesman, Reverend Dr. Samuel Burchard, made this fatal statement: “We are Republicans, and don't propose to leave our party and identify ourselves with the party whose antecedents have been rum, Romanism, and rebellion.” Blaine did not notice Burchard's anti-Catholic slur, nor did the assembled newspaper reporters, but a Democratic operative did, and Cleveland's campaign managers made sure that it was widely publicized.
As if Yankee Republicans of the time more-or-less equated "Romanism" (Roman Catholics) with "Rebellion" (Southrons).
So as I admit, I don't know.