I have seen posts on FR by 'Christians' claiming that RCs are not really Christians ...
The “Church” is the Roman Catholic Church. Those Christians to whom you refer are certainly Christians but they are not Catholics. Considering, as I do, atheists and agnostics (and nazis and communists and a number of other “ists”) as the enemies of my Lord and Savior and that my separated brethren who believe in Jesus Christ as their Lord and Savior are not His enemies and that His Jewish brethren (our older siblings in faith) are also not his enemies (given His Father’s promises to Abraham, among other things), I make it a practice (not always successful) not to argue here with practitioners of other forms of Christianity or of religious Judaism. I specifically decline to accept your invitation extended to me: “Let’s you and he fight.” When he and I have vanquished the enemies of our Lord, we shall have earned the right to disagree with one another in public because the appreciative audience for such quarrels will no longer have the opportunity to enjoy the mud wrestling.