In the case of a married woman who takes a birth control pill for a theraputic purpose, and who also has sexual relations with her husband while on the pill:
The act of taking the medication to treat the medical disorder has a good moral object, treating an illness (or whatever the problem may be). But the woman is not obligated to have contracepted sexual relations as part of her treatment for the disorder. She chooses to have contracepted sexual relations, even though she could refrain. Since these are two separate choices, the contracepted sexual relations cannot be treated as a side effect or an unintended consequence. But the attitude of modern society, which has seeped into the thinking of many Catholics, is that refraining from sex is unthinkable, as if one did not have a choice.
This is not like the case of indirect abortion, where the death of the prenatal occurs necessarily, unintentionally, and not as part of the moral object. The woman chooses to take a contraceptive and to engage in contracepted relations. She is not obligated to do the latter. So there are two moral objects, one good and the other evil. An evil moral object is not an unintended side effect.
The discussion by Pope Pius XII did not permit contraception in all theraputic cases, as the full text shows. Also, his words were not an act of the Magisterium, and were spoken prior to HV, EV, VS, and the CCC. So it is not a tenable theological position to try to modify or nullify the definitive and irreformable subsequent teaching of the Magisterium based on an earlier discussion in a speech.
Regarding the above, how do we incorporate this statement into the behavior in question? Which is the act that deprives the sexual act of procreative meaning in the scenario discussed by Pope Pius XII: the taking of the pill or the engaging in intercourse? If taking the pill is the deprivation then would this mean that the taking of the pill wouldn’t be allowed regardless of whether or not one has intercourse? This doesn’t seem to be the case, because so far there hasn’t been a question about just taking the pill, only about engaging in intercourse after having taken the pill.
Is it the case that a later act (intercourse) makes a prior act (taking a pill for therapeutic reasons) to become morally bad? Or is it the case that an act (intercourse) is morally bad when sterile?
The two deliberate choices to take the pill and to engage in sexual relations is what causes the sexual acts to be deprived of the procreative meaning.
The other consideration is that abortifacient contraceptives, used for an extended period of time, by a woman who is sexually active, is likely to cause an early abortion. It is absurd to say about this loss of life that it is a side effect, or an unintended consequence. Two deliberate types of acts (taking an abortifacient contraceptive and engaging in sexual relations) combine to cause the death of an innocent prenatal. Do you really believe that these deaths are moral because the woman did not wish to refrain from sexual relations while she was on a medication?
The problem here is that sex has become such a high value, disproportionately so, due to the influence of secular society, that no one can even imagine refraining from sexual relations in order to avoid sins of contraception and abortion.