Well said.
By the way, the “release of seed”, as one poster above put it, is not the sole basis for determining if a sexual act in marriage is moral. There is no basis in Catholic moral theology for the claim that, as long as the husband completes the act within natural intercourse, that all else is moral.
Each and every sexual act in a marriage needs to be open to the possibility of conceiving a child. In other words, each and every marital act must of necessity retain its intrinsic relationship to the procreation of human life. So sexual acts that are inherently non-procreative are inherently immoral.
As Pope Pius XII so aptly said (in address to midwives) –
“the spouses must know how to keep themselves within the limits of a just moderation. As with the pleasure of food and drink, so also with the sexual, they must not abandon themselves without restraint to the impulses of the senses…”
“The right rule is this: the use of the natural procreative disposition is morally licit only in matrimony, in the service of, and in accordance with, the ends of marriage itself… And this law, so very reasonable, concerns not only the substance, but also the circumstances of the act, so that, even when the substance of the act remains morally safe, it is possible to sin in the way it is performed.”
“If nature had aimed exclusively, or at least in the first place, at a reciprocal gift and possession of the married couple in joy and delight, and if it had ordered that act only to make happy in the highest possible degree their personal experience, and not to stimulate them to the service of life, then the Creator would have adopted another plan in forming and constituting the natural act. Now instead, all this is subordinated and ordered to that unique great law of the “generatio et educatio prolis,” namely the accomplishment of the primary end of matrimony as the origin and source of life.”
Procreation is the primary end of marriage and the marital act. Marital sexual acts must be of the procreative type; otherwise, the substance of the act is morally disordered (i.e. the act is intrinsically evil).