"If it’s acceptable to use abbreviations for Protestant Churches, it’s acceptable to use them for Catholic churches." They are both acronyms, not abbreviations. The difference is that OPC is a acronym actually used by the Orthodox Presbyterian Church and lacks the history of prejudice, suppression and terrorism that the RC does.
OPC is not the acronym you used before. Use OPC all you want, just like others will continue to use RC. Neither term is gutter language like your other abbreviation.
And neither term contains any "terrorism."
Geesh.