I won't work through the encyclical's argument here, but I will point to one rather prophetic piece of it as an argument in its favor. Pope Paul made four predictions about the effects that widespread use of artificial birth control would have on society:
- a general lowering of moral standards;
- increased marital infidelity;
- the reduction of women to instruments for the fulfillment of male desire; and
- public authorities engaging in coercive population planning programs.
Let's see, how'd he do?
Since 1968, have we seen a general lowering of moral standards? Do we see an increase in sexually explicit material in films and TV? An increasingly "oh well" attitude toward profanity? An increase in kids cheating in school and feeling bad, that not they've done wrong, but that they've been caught? Check. (You might ask, "What does contraception have to do with profanity and cheating in school?" There are lots of dots to connect between the two, but let's just note for the moment that the pope was right about the result.)
Since 1968, have we seen increased rates in adultery, including an increase in women cheating on men? Check.
Since 1968, have we seen women increasingly made into sex objects? An enormous rise in consumption of pornography? An increased sexualization of women in the media, at increasingly younger ages? (Two years ago MTV cancelled a show detailing the sex lives of teenagers because many complained it amounted to child pornography.) Check.
Since 1968, have we seen Western governments pushing birth control in other countries and even making monetary aid dependent on implementing these "family planning" programs? Have we seen the US government forcing employers to pay for contraceptives, even when it violates their consciences? Check.
In any scientific experiment, you consider your hypothesis proved if the results of your experiment are as you predicted them. So, if Pope Paul was right about the negative consequences that an increased use of artificial birth control would have on society, is it at least within the realm of possibility that he (and the Church's steadfast two millenia tradition) might have been right on the nature of artificial birth control itself? Just maybe?