Since no one had to pay to have an Irishman, as they did slaves, the Irish were considered expendable or were almost always given the most dangerous jobs where a person could get killed. Slave owners didn't want to lose their investments on black slaves.
That 2nd rendition of the Klan, Birth of the Nation Klan indeed was anti-Catholic, they held marches about it and probably gave out brochures, I think I saw some on the web.
Even Kennedy as we all know, JFK put up with some anti-Catholic bigotry; and to be fair, some books report young JFK may have used a pejorative in his time. We were not all perfect.