The answer will be found in Pascendi Dominici Gregis, promulgated by St. Pius X in 1907. It condemns Modernism as a Heresy. Then get a good book or two which explains Modernism and you will have your answer. Quick summary: Modernism believes that there is no Truth. That may be true for you, but it isnt for me thinking. The Catholic faith before Vatican II insists that it was True because God revealed it and He can neither deceive nor be deceived. Vatican II claimed that Truth wasnt Absolute, and it could therefore change, which of course is wrong. Thats my understanding of it.
Sorry for butting in, but I researched this pretty thoroughly a few years ago.
Yes, that is helpful to know. My immediate question is Vigano. Does he
1. openly espouse the view you describe
2. probably espouse it but dances around it in public writings
3. in his writings accept the validity of Vatican II but reject its misapplication (like benedict)