It would have been less pernicious if Vatican II had simply said, "yes, we're teaching this new thing" ... instead of claiming that the novelties and Modernist interpretations in there were just the same old stuff properly explained.
This attack undermines all of Catholic faith. Hmm, I used to believe this with the certainty of faith, but now I guess I had it all wrong and misunderstood it, so evidently my certainty of faith was misplaced. This leads directly to doubts about the faith and the Church's teaching authority, from which the formal motive of supernatural faith derives. So it isn't an attack on one dogma only, but on the very foundation of all dogma. It's, as St. Pius X taught, the synthesis of all heresy because it attacks the very foundation of all faith.