Here is a very good snippet from this column written by Christopher O. Tollefse called, Speaking Truth to Evil (in Public Discourse), on how certain acts not matter what the circumstance or the good one wishes to attain, is always wrong by the virtue of choosing that object, an evil object i.e (say) murder, Rape, Contraception ect.
Only "Unjustified" False Assertion?
The first challenge has to do with the nature of moral absolutes, such as the absolute norm against murder, or, as I believe, the absolute norm against lying. Hadley Arkes and Francis Beckwith, while seeming to agree that these are moral absolutes, have both argued that absolute norms such as these contain within them a moral qualifier. The prohibition on murder is a prohibition on unjustified killing. Likewise, the prohibition on lying is on unjustified false assertion.
Yet no critic, speaking from the Catholic intellectual or faith tradition, has drawn the obvious conclusion from this that therefore the (absolute) norm regarding adultery is a norm against unjustified extramarital congress; or that the (absolute) norm against contraception is a norm against unjustified prevention of conception. And this is hardly surprising, for it is widely recognized that this is not, in fact, the nature of these norms.
As John Paul II labored to explain, there are acts which, independently of their further ends, or of their circumstances, are wrong precisely in virtue of the object chosen. That object—the form of behavior settled upon by the agent—is incompatible with the human good, including the human being's ultimate orientation to God. Choices of these sorts are wrong everywhere and always. Their objects are designated "intrinsically evil" precisely to indicate that their moral character can be recognized by considering only the object of the act itself (other questions, concerning the gravity of any particular violation, for example, will require attention to ends and circumstances).
One does not, therefore, look to whether extramarital intercourse is being performed at the right time, with the right person, in the right way, or with a view to some good end (perhaps an abortionist will give up his trade if a married woman were willing to be his mistress, thus saving the lives of many unborn in the area). Rather, one recognizes that the choice of such intercourse is incompatible with the human good because of its violation of the good of marriage, full stop. In asserting that adultery is always and everywhere impermissible, then, the tradition does not hold that adultery is "unjustified extramarital intercourse," but that it is simply extramarital intercourse as such.