I don’t know if I would call it “Protestant” but if someone showed me this liturgy prior to Vatican II, I would have definitely called it non-Catholic and would have had to confess if I attended it of my own free will.
Interesting. ‘Non-Catholic’ - when used to describe a rite of the Mass that has been validly promulgated by Rome and signed off by the Pope - is quite simply an oxymoron. May as well speak of circular squares or four-angled triangles as a Non-Catholic Mass that has been promulgated by Rome itself.
As for having to confess - well, if you’d attended a liturgy that followed word-for-word the EF prior to the Council of Trent you would also have had to confess that - as it was not
at that time a valid rite of liturgy and so it would not have been proper for you to attend at any time
prior to its promulgation by St Pius V. Afterwards, of course, it was fine.
That’s simply a matter of canon law though, not a reflection on either the TLM or the forms of Mass that existed prior to it - after all, a number of them were allowed to continue alongside the TLM.
Rather like if you fasted for three hours prior to communion in the 1850s that would’ve been a violation of both Canon law and of a precept of the Church. You would’ve had to confess it at that time because Canon Law and precept stipulated a midnight fast.
Whereas if you’d done so in the late 1950s you would’ve been fine, had nothing to confess and committed no sin, because by then the venerable Pope Pius XII had altered canon law (and hence the fasting precept) to stipulate three hours.
Canon law and the details of the precepts of the Church are at least in part DESIGNED to be changeable, and have certainly been changed frequently enough. So it is with forms of liturgy - the prayers of the Mass have actually been altered numerous times, even between Trent and Vatican 11. And the Church’s OTHER form of liturgy (people keep forgetting that Liturgy of the Hours is ALSO liturgy) was much more comprehensively revised under St Pius X, ironically enough for the society that bears his name.
Main point being - Canons of Trent, Seventh Session - stipulate that it is ANATHEMA to suggest that the forms (as there were several in existence, so not only referring to the TLM) used by the Church in conducting the Holy Sacrifice of the Mass are in any way incentives to impiety among the faithful.
So any criticism in that vein of the form of the NO - such as calling the prayers themselves ‘Protestant’ (since the heresy of Protestantism surely fits under the definition of impiety) potentially means anathematisation of the critic.
Sure, Pope Benedict himself criticised the NO, but went no further, if memory serves, than calling it banal and an on-the spot fabrication or words to those effects.
