Here's what they said:
In addressing this issue we must begin by recalling that when asked about marriage, Jesus said: “Have you not read that from the beginning the Creator ‘made them male and female’?” (Matthew 19: 4) Scripture, biology, and the Natural Law reveal that it is God’s design that the two sexes are complementary. While Americans have a laudable desire to treat all people with equality, equality does not mean interchangeability. The well-intentioned desire to accept any and all circumstances is misplaced when it applies to an eternal institution such as marriage. We would further note that God’s plan for marriage is for the wellbeing of men and women. However it is also, and especially, for children.
Notice that the bishops separate the supposedly inseparable unitive and procreative ends of marriage in their statement. Biological complementarity is positioned as an isolated end, almost a first principle, and procreation is added as a "however" and an "also". Even adding the word "especially" doesn't help because identifying progeny as "special" still - if not further - separates the procreative.
Modern Catholic teaching on marriage is rife with this kind of language and it descends from a novel insertion into the 1983 Code of Canon Law known in Latin as "bonum coniugum" or the "good of the spouses", an insertion which caused renowned canonist, Cormack Burke (and others) to scramble to manufacture a justification.
The essential squabble is whether the "bonum coniugum" is an end or a property (good) of marriage. Seen as an "eternal good" - in that marriage is a path to heaven - the good of the spouses as an end of marriage can be easily admitted. But seen as an earthly good - which it is by most - simply translates into mutual satisfaction and spousal happiness, which is really no more than one of the "goods" of marriage, and only a potential good at that.
Theologians may squabble over whether the 1983 canonical insertion of the "good of the spouses"* was a good idea or not, but the net effect was an immediate avalanche of annulment requests, the wholesale abandonment of the sacrament of marriage by the following generation, marriages which see children as an option, accessory, appendage, or even a hindrance to marital happiness, and a fast track to the legalization of a marital union where spousal happiness is all that matters.
What's really sad is that the bishops do this (separate the unitive and procreative) thinking they are actually defending traditional marriage. Once upon a time our Church actually taught that children were the reason for marriage. They were not "however's", "also's", or even "especially's". They were "primary".
This belief descends directly from the first account of creation where in a single act God creates "them male and female" and commands them to be "fruitful and multiply". There is no separation. There is no "oh by the way" when it comes to the duty to be fruitful. There is no "however" or "also". Man and woman are created married and fruitful in one act.
This is still why our Church does not recognize a marriage as valid - even after the wedding and all the proper sacramental form has taken place - until the husband engages in a potentially procreative act with his new bride, i.e. "consummates the marriage".
We say "potentially procreative act" because all procreative acts are only acts and only potentially procreative. Whether or not a child is conceived is beyond the power of the two to effect. They can only engage in the act.
AS THE CHURCH GOES, SO GOES THE WORLD.
AS THE CHURCH GOES, SO GOES THE WORLD.
As an aside, this draws into question whether or not Catholic couples are actually married when their first conjugal act is intentionally sterile - whether by natural means or not. Avoiding children through periodic continence (NFP) is allowed as an exception for grave reasons ("just cause" says the Catechism). If couples have grave reason not to conceive from the outset then the question is raised should the marriage proceed...or can there even be a marriage.
(Note: Barrenness has never been an impediment to marriage and is a consequence of the Fall.)
* Can. 1055 §1. The matrimonial covenant, by which a man and a woman establish between themselves a partnership of the whole of life and which is ordered by its nature to the good of the spouses and the procreation and education of offspring, has been raised by Christ the Lord to the dignity of a sacrament between the baptized.