Why does the RCC so passionately reject this practice?
Those that reject the Rule of Scripture in norming tend to do so not because they reject Scripture or have an alternative that is MORE inerrant, MORE the inscripturated words of God, MORE reliable, MORE objectively knowable, MORE unalterable, MORE ecumenically embraced as authoriative, MORE above and beyond and outside all disputing parties. Rather the rejection is because the protestors rejects accountability (and thus norming and any norm in such) in the sole, singular, exclusive, particular, unique, individual case of it itself alone, uniquely, individually.
From The Handbook of the Catholic Faith (page 151), "When the Catholic is asked for the substantiation for his belief, the correct answer is: From the teaching authority. This authority consists of the bishops of The Catholic Church in connection with the Pope in Rome. The faithful are thus freed from the typically Protestant question of 'is it true' and instead rests in quiet confidence that whatever the Catholic Church teaches is the teaching of Jesus Himself since Jesus said, 'whoever hears you hears me'." The Catholic Church itself says in the Catechism of itself (#87): Mindful of Christ's words to his apostles: “He who hears you, hears me”, The faithful receive with docility the teachings and directives that their pastors give them in different forms."
Since it itself declares that it itself individually and exclusively is unaccountable and that whatever it itself exclusively and currently says is just to be swallowed because it itself individually and currently is saying it, then the entire issue of norming (and the embraced norma normans in such) has simply been denied (for itself). The issue has been changed from truth to the unmitigated power (claimed by itself for itself, exclusively). THIS is why Catholics will never engage in the issue but rather run to defend this unmitigated, unaccountable, God-like POWER that the RCC claims for itself exclusively that "trumps" the issue of truth and accountability, they claim.