One thing that contraception has done very well is to separate the connection of the marriage act from procreation, not a big surprise, as that is what it is intended to do. However, I do not just mean that sex and babies are separated in the physical sense, as in if you use "protection" you can avoid pregnancy. I am suggesting this separation has affected our society's very understanding of the purpose of marriage, sex and babies.
A recent poll of married couples suggests that children are perceived as irrelevant to finding happiness in marriage. It is now completely common, accepted, and expected for people who are not married to have babies and for people who are married to choose to avoid having babies. Further, our separation of marriage, sex and babies has resulted in "valid" marriages of same sexed persons, and conceptions without sex (in vitro fertilization, donor eggs, surrogate mothers, and cloning). Perhaps you agree with these cultural shifts, perhaps you do not, but one thing follows another, and the point is that contraception works. We have effectively separated what was meant to be intrinsically joined.
"What God has joined, let no man separate," we hear in the traditional wedding as man and woman are joined as husband and wife. God joins a man and a woman in marriage, with the resultant sex and babies. This is God's design, but in our limited human thinking, we have separated all of the above so that today our cultural understandings of marriage, family, husband, wife, mother and father are confused.
This is not about married couples who do not have children or have smaller families, due to their God given vocations, or because of infertility. This is about the confused, shocked, and dismayed reactions that confront couples in loving marriages when they announce that *surprise* they are having a baby!
For some reason, even faithful Catholics seem to think that married couples who are having babies are simply making a lifestyle choice. The idea is that couples who have been blessed with many children are doing it because...they always wanted a big family...they love kids...they are really organized and hard working...they are trying to "prove" something...they are trying to keep up with the big family down the block...et cetera. There is always some planned reason that must be attached to the excessive procreation in some families, reasons that ignore the simple connection between marriage, sex and babies.
Those who choose to simply follow God's plan for marriage, as the Church so beautifully describes, may find that the babies just come. It really is as simple as that, no further explanation needed.