Fr. Joe Pat Breen and his followers are citing the primacy of conscience in moral decision making. I am not enough of a theologian to argue the point academically, although others can (see Dr. Janet Smith below). I do want to speak from one area in which I am an expert: my own experience. I have to say that the biggest mistakes and even sins that I have committed have come as a result of my following what my conscience was telling me in contrast to the guidance of legitimate authorities: my parents, my Church, my friends, good old common sense, etc. I know that I cite my conscience as authority for things that I want to do when I can't get approval any other way. My conscience is useful in this way. It is much more susceptible to my own reasoning and justification than outside authorities. Citing conscience makes me feel righteous about fundamentally selfish decisions. I put everybody else in the wrong when I cite my conscience. I become a hero for doing my own thing. I fall for the allure of doing what I want to do and being self-righteous about it.
The problem arises when I come back to reality and see what my conscience has led me into. Even though my conscience can change my perceptions, it can't change reality. I think to myself: "What was I thinking?" I see an abyss opening right in front of me. Time and time again, I catch hold of an authority outside of my own reasoning and pull myself back from the abyss. As a Catholic, I generally find that anchor of authority in Confession. It is humiliating to admit that I can be so blind. It has usually been my conscience that has blinded me. After a number of these humiliations, my conscience slowly learns obedience and becomes a better guide.