Procreation and unity - or, contraception part II

This post is not as "family-friendly" (that is, child-appropriate) as most on this blog

Reading my way across the internet today, I came across a very clearly and eloquently worded explanation of the nature of sexual intimacy (actually this writer has consistently been, in all that I have read so far, quite clear, logical, courteous, and sensitive to beauty, which makes for very enjoyable and edifying reading).

"...human sexual nature is not a collection of facts that have no meaning until we freely assign them one. Sexual intercourse has a natural teleology; it is ordered to procreation. This natural end provides a context which itself assigns a meaning to the sexual act. This meaning is “natural” in the sense that it “presents itself” to the mind of a sufficiently intelligent participant without requiring any decision on his or her part. If I make love to a woman, it means “I choose you to be the mother of my children.” This, and only this, is directly and naturally signified by intercourse. However, for an intelligent being, able to consider the future, it has profound implications. Children require a family, so the sexual act implies an irrevocable commitment; it initiates a new society consisting of the spouses and their prospective children. In the conjugal act, the spouses pledge their allegiance to this society—this also is virtually contained in the act’s one natural meaning." - In Defense of Patriarchy, by bonald

The unitive nature of the act, then, is bound to its procreative nature. This is an assertion I have heard many times but never completely understood. For example, I have struggled to understand why some (including, officially, the Catholic Church) believe that it is wrong for a married couple to use contraception. After all, the married couple has already, in other ways, signified and established the union between them, and they are most likely intending to bring that union to fruition at some point in the future. The man is still choosing that woman to be the mother of his children (and vice versa) - just not yet.

And yet I can see, symbolically, the contradiction in that. Symbolically, contraception is truly a rejection - a rejection of the full nature of sexual intercourse and thus a reduction of its meaning, and a rejection at a very basic level of the other person. If sexual intimacy is unifying by nature and not just by convention, then contraception interferes with that union by preventing the partners from completely giving themselves to each other. In the middle of what ought to be an utterly self-surrendering act, in which each becomes the other's, the man does not give and the woman does not receive. Considering that some (beautifully expressed over at Like Mother, Like Daughter) have defined masculinity and femininity by the roles of being the first giver and the one who receives in order to give again, respectively, this is a serious issue. Symbolically, not just physically, contraception establishes a barrier between two people even as they are seeking unity, by short-circuiting the inherent procreative nature of sexual intercourse on which the unitive nature is founded.

What, then, are the practical implications of that symbolism? Does it matter morally, emotionally, or spiritually - or is it just a beautiful ideal picture? I'm not sure, to be honest. I don't know that it is inherently wrong for a married couple to use contraception, but I am having a hard time coming up with an argument as coherent and beautiful as the one above. Everything begins to sound like an excuse or a rationalization rather than a unified understanding of the nature of sexual intercourse within marriage as God designed and intended it, which is insufficient for someone who desires to follow God wholeheartedly in this area of life just as in any other. Do any of you have thoughts on this? Can you offer me a complete picture of the nature and purpose of sexual intimacy and how that informs our behavior, as opposed to a "I'm sure it is fine to use contraception now, since you're committed and planning on having children later?"