Why you cannot decide what is and is not tradition and why Vatican II May Have Been Unwise in Parts, But Not Heretical, Per Impossible

---from APA citation. Bainvel, J. (1912). Tradition and Living Magisterium. In The Catholic Encyclopedia. New York: Robert Appleton Company. Retrieved November 11, 2009 from New Advent: http://www.newadvent.org/cathen/15006b.htm

"The living magisterium, therefore, makes extensive use of docuмents of the past, but it does so while judging and interpreting, gladly finding in them its present thought, but likewise, when needful, distinguishing its present thought from what is traditional only in appearance. It is revealed truth always living in the mind of the Church, or, if it is preferred, the present thought of the Church in continuity with her traditional thought, which is for it the final criterion, according to which the living magisterium adopts as true or rejects as false the often obscure and confused formulas which occur in the monuments of the past.

"Thus are explained both her respect for the writings of the Fathers of the Church and her supreme independence towards those writings--she judges them more than she is judged by them. Harnack has said that the Church is accustomed to conceal her evolution and to efface as well as she can the differences between her present and her former thought by condemning as heretical the most faithful witnesses of what was formerly orthodoxy.

"Not understanding what tradition is, the ever-living thought of the Church, he believes that she abjured her past when she merely distinguished between what was traditional truth in the past and what was only human alloy mixed with that truth, the personal opinion of an author substituting itself for the general thought of the Christian community.

"With regard to official docuмents, the expression of the infallible magisterium of the Church embodied in the decision of councils, or the solemn judgments of the popes, the Church never gainsays what she has once decided. She is then linked with her past because in this past her entire self is concerned and not any fallible organ of her thought. Hence she still finds her doctrine and rule of faith in these venerable monuments; the formulas may have grown old, but the truth which they express is always her present thought.

http://www.newadvent.org/cathen/15006b.htm

Extrapolating then, Vatican II was called by a legitimate Pope (as even Sede Fr. Noel Barbara admits) and an unprecedented  vast assemblage of the world's bishops who were validly consecrated. Therefore the Pope and Bishops together could not, a priori, promulgate heresy since the Holy Spirit protects against heresies in a negative way, so to speak.

The Spirit does not guarantee wisdom or even protect against recklessness; He protects only against heresies when a Pope and Bishops act in a Church Council and ecuмenical.  A priori, according to Catholic theology, the Church in such a situation cannot birth heresies. Even if the Pope could defect, the official reception of the Council's acts by the assemblage of bishops convoked in Council would guaranteeing such acts as free from heresies.