primacy of conscience: when this term is used to over-ride the teachings of Tradition and Scripture, or any infallible teachings, then it is heresy. But when it is used to encourage persons who have formed and are still forming their conscience in accord with Tradition, Scripture, Magisterium -- so that conscience is above social pressures, peer pressures, culture, personal weaknesses, etc., then is it true. Conscience is primary when compared to these other lesser things, but not when compared to the Word of God.
the teaching against abortion is infallible: it is clear from Tradition and Scripture that abortion is gravely immoral, it is also a teaching of the ordinary and universal Magisterium, and it was infallibly defined as always gravely immoral by Pope John Paul II and the Bishops of the world in Evangelium Vitae.
the teaching that homosexual acts are always gravely immoral is clear from both the Old and New Testaments, it has also been the consistent teaching of the Church throughout the centuries, so this teaching is infallible under the ordinary and universal Magisterium. So also is the teaching that the orientation is intrinsically disordered; it is not good, nor the will of God.
However, there may be other related teachings that are still under development. For example, as to the homosexual orientation and its causes, and as to priests who are homosexuals and their status in the Church. Faithful Catholics have a range of opinions and ideas about how society and the Church should treat homosexuals.
So some teaching on this subject fall under the Sacred Magisterium to which one must give sacred assent, but other teachings are under the Ordinary Magisterium, from which one might faithfully dissent (if the basis for dissent is Tradition or Scripture or prior teachings of the Magisterium).
Concerning contraception, Humanae Vitae condemned contraception, but permitted natural family planning so far as to permit NFP to be used very strictly, in an attempt to avoid all conceptions, if the couple has a grave reason. This doctrine was later developed, so that NFP could be used less strictly, not attempting to avoid all conceptions but to space out one's children, if the couple has only a just reason (a lesser standard). Also, new methods of NFP continue to be developed. And the teachings on this subject may develop further.
Now the teaching against contraception has never been infallibly defined, but it does, in my view, fall under the ordinary and universal Magisterium (requiring sacred assent): contraception is immoral and NFP is moral. There may be some further development of doctrine, but I don't think faithful dissent can go so far as to approve of artificial contraception.
Faithful dissent, in my view, is limited to the teachings of the Ordinary Magisterium and only then when one's dissent is based on Tradition or Scripture or Magisterium. It is sometimes difficult to tell which teachings fall under the ordinary and universal Magisterium, but such teachings so require sacred assent.
Typical dissent against Church teaching is not faithful dissent, partly because it is dissent from teachings of the Sacred Magisterium, and partly because people dissent due to the influence of their culture and society, not due to their understanding of Tradition, Scripture, Magsterium.