The Ford-Grisez Thesis
From 1963 on, theologians seeking to justify contraception, after observing (correctly) that the teaching had not been formally defined, proceeded to infer (erroneously) that the doctrine had not been infallibly taught.  The conditions under which the ordinary Magisterium of the bishops dispersed throughout the world can proclaim the teaching of Christ infallibly have been articulated by the Second Vatican Council. Ford-Grisez argue that Humanae Vitae meets those criteria, thus making the Church doctrine a divinely guaranteed teaching.
They make an important point. Frequently, dissenters start with the assumption that teachings not formally defined are not infallible. This is not true. Many Catholic teachings are de facto infallibly taught, even though not formally defined. Lumen Gentium (No. 25) reads:
Although the bishops individually do not enjoy the prerogatives of infallibility, they nevertheless proclaim the teaching of Christ infallibly, even when they are dispersed throughout the world, provided that they remain in communion with each other and with the successor of Peter and that in authoritative teaching on a matter of faith and morals they agree in one judgment as that to be held definitively.
The declaration, as Council debates indicated, extends ordinary infallibility in the Church not only to matters formally revealed (for example, the divinity of Christ) but also to things virtually revealed (for example, Mary’s Immaculate Conception), to what is necessarily connected with revelation (for example, the existence of a natural moral law), to things that are to be believed, and to things that are to be done.
Christ did not win all his public debates over what he was revealing. The Church has also learned that the validity or certainty of a teaching does not depend for acceptance on its perusability or on the solemnity of the preaching. Faith in the given teacher usually settles the argument for the believer.
What they are saying is either that human judgment stands above the law of God or that the Catholic Church is lying when it claims divine authority for its moral teaching (Cardinal O’Boyle, NC News, Sept 5, 1968).
Responding to Charles Curran et al’s Dissent in the Catholic Church, Joseph Constanzo S.J. responded with:
The insistence [of dissenters] that theologians are intrinsic to the ecclesial Magisterium is the most rootless of all protestations. There is no warrant for it in the mandate of Christ, neither explicitly, implicitly . There is no evidence of such a role for theologians in the writings of the Fathers of the Church nor in any of the official documents of the Church, papal or conciliar. And for all the dissidents’ facile rhetorical references to Vatican II, the Council Fathers never graced them with a distinct classification or separate consideration as they did with the Roman Pontiff, the Bishops, the Religious, laity and priests. Indeed, the word itself “theologians” appears only once among the 103,014 words of the sixteen official texts promulgated by the Ecumenical Council. Considering the centrality of the dissidents’ concept of the role of theologians as “an intrinsic element in the total magisterial function of the Church” to their ecclesiology, it sees that they have been slighted by a Council celebrated for its formulation of the collegiality of bishops and by those very bishops who were accompanied by periti” (Thomist, October 1970).
[Paul VI himself wrote:]
Unfortunately among us some theologians are not on the right path. 
Some have recourse to ambiguous doctrinal expression and others arrogate to themselves the permission to proclaim their own personal opinions on which they confer that authority which they more or less covertly question him who by divine right possesses such a protected and awesome charism. And they even consent that each one in the church may think and believe what he wants. (Pope Paul VI, Bogata, NC News, August 24, 1968)
There are still those today, echoing the discredited words of the 60s era self proclaimed alternate Magisterium, who hold that the church should be ruled by a democratic principal; that majority should rule. To those who hold such a position, contrary to the faith of their baptism and the creed that they profess, I would remind them that the Church has already had a brief experience with majority rule; ecce homo (behold the man). Such votes carried the day then…
Jesus of Nazareth - The People Decide