But a woman who is taking medication to treat a condition is not proposing to hinder procreation, either as a means or an end in itself. She is not commiting an act of contraception.
The end proposed by the person is the finis agentis (first font: intention). VS is very clear that intention does not justify any intrinsically evil act. CCC explicitly teaches that legitimate intentions do not justify contraception. If contraception were defined by the intention of the person, it would be justified by a non-contraceptive intention.
The intentionally-chosen act also has its own end, the finis actus (second font: moral object). By choosing an act inherently ordered toward a contraceptive end, the person intentionally contracepts. And this is true even if the contraceptive is a means to a good end.
The same analysis applies to direct abortion to save the life of the mother. The person does not intend the death of the prenatal (finis agentis), but by intentionally choosing an act ordered to that proximate end (finis actus), the person necessarily chooses the act, its ordination, and its end.
The example of euthanasia is quite definitive in the distinction between intention and object. Euthanasia by definition (Evangelium Vitae) is murder with the medical purpose of relieving all suffering. EV states that this purpose is the good intention of the act, and yet the act is intrinsically evil. So it is not possible to claim that a good intention, including a good medical purpose, redefines an act as not intrinsically evil.
You need to brush up on your undertanding of double effect. A person can choose an act this is morally good or neutral (eg taking medication) that may also have an unintended and unavoidable secondary effect (inhibiting fertility).
A person can deliberately chose an act that has a contraceptive end, as long as that end is not directly intended, not the means to the good end, and there is proportionate reasons to do so.
Which brings us directly back to HV: “…the Church does not consider at all illicit the use of those therapeutic means necessary to cure bodily diseases, even if a foreseeable impediment to procreation should result there from—provided such impediment is not directly intended for any motive whatsoever.”
This is all about double effect and whether contraception is directly intended or merely an unintended secondary effect.
The therapeutic interventions spoken of in HV are cases of indirect sterilization. The term “directly intended” refers to the font of the object (finis actus). To intentionally choose an act directly ordered toward a contraceptive end is the definition of intrinsic evil. The term “any motive whatever” refers to the intention or purpose chosen by the person (finis agentis). So HV 15 is saying that, to be moral, such an act must not be intrinsically evil (not directly intended) and that intrinsically evil acts are never justified by any motive.
You are saying the opposite of HV 15, that the motive to treat a disorder justifies the deliberate choice of an act with a contraceptive end (finis actus). Such a choice defines the term “directly intended”.
The principle of double effect NEVER justifies an intrinsically evil act. And intrinsically evil acts are never defined by intention (finis agentis). Every intrinsically evil act is intentionally chosen (deliberately chosen), but in choosing the act, the person necessarily chooses its nature and its object. The term “directly intended” refers to the intentional choice of an act directly ordered toward its object, and when the object is evil, the act is intrinsically evil.
The chosen act is never morally neutral; to make such a claim nullifies the font called moral object.
“A person can deliberately chose an act that has a contraceptive end, as long as that end is not directly intended, not the means to the good end, and there is proportionate reasons to do so.”
The deliberate choice of an act that has a contraceptive end has been condemned by the Magisterium. The Church condemns “actions which are in themselves (that is, by their nature and condition) ordered toward a contraceptive end” regardless of the intended purpose of the person who acts (agentis). [Quaecumque Sterilizatio, March 13, 1975, AAS 68 (1976) 738-740]
The choice of an act with a contraceptive end (finis actus; the moral object) is what the Church means by “directly intended”. The intentional choice of the act, directed toward an evil end, is an intrinsically evil act by definition.
I should also point out that the type of medication considered here is abortifacient, and if the couple remains sexually active, some actual abortions may occur. The fact that some prenatals die as a result of this choice effectively refutes the unintended side effect argument. The medication could be taken while avoiding sexual relations, thereby making the choice neither contraceptive nor abortive.