In Dr. Philip Blosser's weblog, after O'Leary's terrible criticism of the most positive aspect of Paul VI's pontificate (Humanae Vitae), I said that "It wasn't HIS decision -- he COULD NOT write anything else, even if he wanted."
The "good Father"'s answer was that :
you should say in strict logic that Vatican II also COULD NOT write anything else, even if it wanted. That's the wonder of the conciliar privilege, that's the glory of Catholicism, that's the beauty of Christendom! ... Or rather, an Ecumenical Council enjoys far greater authority than a papal encyclical (especially an encyclical rejected by the church).
Well, all I can say is that Vatican II apparently did not explicitly state anything CONTRARY to Catholic Tradition, though it did change many policies (which could be changed back today) -- the absence of transitional documents which could explain to the Catholic faithful what traditions (with lower t) may be changed and what is part of the unchangeable Tradition is one of the dramas of contemporary Catholicism and of the causes of the feeling of doctrinal centrifuge which seemed to bring the Church to the brink of collapse in the 1964-1979 period and it is well explained by Fr. Ripperger in this wonderful article. I will not mount a wholesale defense of Vatican II here: you will have to find another person. I think it was an unfortunate event, but not outright heretical.
Paul VI, of course, was very wise to forbid the Council to discuss artificial contraception (the chapter on demography in Gaudium et Spes is particularly ridiculous) and it is a sign, as Humanae Vitae itself, as well as Mysterium Fidei, of the papal privilege, which manifests itself in the most unexpected times and in the most unexpected occupants of the Petrine throne.