At the Little Catholic Bubble blog site, Bethany writes,
The bodies become fully united at, well, to be blunt, ejaculation in the vagina, thus fulfilling the necessary requirements to allow the potential of reproduction to take place.
And at his Letters to the Catholic Right site, Frank Strong responds,
In fact, this definition, traditional though it may be, takes all of the meaning out of the word union. Think about it: it means that one-night stands are union, and inconsiderate sex from which only the man gets pleasure is union. It means that a woman’s pleasure, while nice, is not necessary for union. Chillingly, it means that rape is union. And it means that a loving, married couple having a transformative bonding experience is not union, if the man is wearing a condom.
And, of course, there's the fact — no small matter — that "the potential of reproduction" cannot be present when one or both members of the "union" are infertile, due to infirmity or age. But the Catholic church and any other church of which I have any knowledge at all has absolutely no qualms about marrying such infertile couples.
As long as they're heterosexual, a male and a female.
Which means that all this elusive, counterfactual, magical-mystical language about "union" and the sacred significance of semen (which requires the passive and receptive vagina as its "natural" repository) is really not about "union" at all. It can't credibly be about union in a church in which the vast majority of heterosexual married Catholics use contraceptives and approve of their use.
It's about stigmatizing, demeaning, dehumanizing, and excluding people who are gay.
Excluding these human beings from the human community and the church.
In the name of God.
And pretending that this entirely hateful objective is somehow sweet and holy, and that we who pursue it are sweet and holy. Particularly when measured against the gays, who are, by definition, the unholy and the bitter.