The teaching is really clear. Anything that intentionally separates the unitive and procreative aspects of the act is intrinsically evil. The things you mention are not why contraceptive acts are evil but are some of the deleterious results of engaging in contraceptive acts.
Can you provide proof of these statements? Each and every marital act must be open to life. Where can I find that contraceptive acts, which are always intrinsically wrong, are less sinful in certain circumstances?
"Could it not be admitted, in other words, that procreative finality applies to the totality of married life rather than to each single act? "
The Pope here sees the issue - the questions of whether marriage should be open to life and whether each act must be open to life are different.
“This was all the more necessary because, within the commission itself, there was not complete agreement concerning the moral norms to be proposed, and especially because certain approaches and criteria for a solution to this question had emerged which were at variance with the moral doctrine on marriage constantly taught by the magisterium of the Church.”
It is not an easy question. The Pope’s commission didn’t all agree.
“Neither is it valid to argue, as a justification for sexual intercourse which is deliberately contraceptive, that a lesser evil is to be preferred to a greater one, or that such intercourse would merge with procreative acts of past and future to form a single entity, and so be qualified by exactly the same moral goodness as these. Though it is true that sometimes it is lawful to tolerate a lesser moral evil in order to avoid a greater evil or in order to promote a greater good,” it is never lawful, even for the gravest reasons, to do evil that good may come of it (18)—in other words, to intend directly something which of its very nature contradicts the moral order, and which must therefore be judged unworthy of man, even though the intention is to protect or promote the welfare of an individual, of a family or of society in general. Consequently, it is a serious error to think that a whole married life of otherwise normal relations can justify sexual intercourse which is deliberately contraceptive and so intrinsically wrong."
Finally, the Pope rejects the idea that contraception to limit rather than avoid births may be acceptable. However he does describe such contraception as a lesser moral evil tolerated to promote a greater good, but rejects this as licit, because it is doing evil so that good may directly come of it.
So the conclusion we can draw is that contraception aimed at makingthe whole of a married life sterile is more sinful than contraception intended to limit the number of births. That’s pretty obvious really - stealing all a widow’s money is worse than taking her purse - though stealing the purse may still be gravely sinful.
