I find this "catholics are not christians" phenomenon fascinating. The best example for it was one of these creationist movies, where they ask totally legit random people if they are christians, and one says: "no, I'm catholic".
Is this a speciation event we are observing? Obviously religions can't reproduce with each other, but, if two denominations no longer consider each other to be the same religion, can they be considered different "species"?