"Bishops, teaching in communion with the Roman Pontiff, are to be respected by all as witnesses to divine and Catholic truth. In matters of faith and morals, the bishops speak in the name of Christ and the faithful are to accept their teaching and adhere to it with a religious assent. This religious submission of mind and will must be shown in a special way to the authentic magisterium of the Roman Pontiff, even when he is not speaking ex cathedra; that is, it must be shown in such a way that his supreme magisterium is acknowledged with reverence, the judgments made by him are sincerely adhered to, according to his manifest mind and will. His mind and will in the matter may be known either from the character of the documents, from his frequent repetition of the same doctrine, or from his manner of speaking."
-Lumen Gentium 25
I have heard some Catholics try to make a case for contraception simply because many theologians rejected Paul VI's encyclical, Humanae Vitae. This is a very weak argument, because the authority of the Church is not (and has never been) with theologians. A theologian can assist the Magisterium and advise them, but the final say and the teaching authority lies solely with the bishops in union with the Pope. While many theologians of the time rejected Paul VI's encyclical, the majority of American bishops stood firmly behind the Pope.
Ralph M. McInerny, in his book What Went Wrong With Vatican II, says:
"In a debate sponsored by the Washington Lay Association, the question quickly became whether Catholics, having listened, were permitted to disagree. In the debate, Triumph magazine editor L. Brent Bozell maintained that any Catholic who does not accept the encyclical denies the Pope, denies the Church, and denies Christ, because he is not so much denying truth as authority. Catholics have an obligation to assent. He said that those who call themselves theologians but don't accept the encyclical should not consider themselves capable of serious theological discussion."
Bozell also said:
"Those priests who refuse to accept and faithfully carry out in their pastoral capacity Pope Paul's encyclical on birth control, should leave the Church. Any person who refuses submission to an authoritative teaching by the supreme pontiff on Faith and morals is a schismatic; and simple honesty, greatly honored in the present age, requires him to acknowledge the state of schism.
Any priest whose reason is not persuaded by the Pope's teaching should pray fervently to be among those whom Christ praised because they 'have not seen, and yet have believed' (John 20:29). If they will not do this, they should cease pretending to represent the Catholic Church. Otherwise, they will be personally responsible for widening the schism and increasing the scandal."
McInerny goes on to write in the book:
"Fellow Triumph editor Michael Lawrence was equally severe in the Washington debate. Lawrence said that those who do not accept the right of the Church to teach on moral questions are simply not Roman Catholics. Further, those who say that Humanae Vitae should be taken seriously, but who would balance the Pope's teaching with their own private conscience, have a 'Protestant view' of conscience. 'A Catholic does not have a free conscience.'
In other words, while anyone is, of course, free to be a Catholic or not, he is not free as a Catholic to reject what the Church teaches. To do so is to cease to be a Catholic."