“The Church, founded on these principles and mindful of her office, has done nothing with greater zeal and endeavor than she has displayed in guarding the integrity of the faith. Hence she regarded as rebels and expelled from the ranks of her children all who held beliefs on any point of doctrine different from her own.
The Arians, the Montanists, the Novatians, the Quartodecimans, the Eutychians, did not certainly reject all Catholic doctrine: they abandoned only a certain portion of it.
Still who does not know that they were declared heretics and banished from the bosom of the Church? In like manner were condemned all authors of heretical tenets who followed them in subsequent ages. There can be nothing more dangerous than those heretics who admit nearly the whole cycle of doctrine, and yet by one word, as with a drop of poison, infect the real and simple faith taught by our Lord and handed down by apostolic tradition.”
Pope Leo XIII Satis Cognitum IX, 29JUN0001896
"Lex orandi, lex credendi, lex vivendi."
Great zeal? Only that of the (other?) Jews, and (other?) Communists.