S
SMGS127
Guest
Because the marital act must always ‘conclude’ (conclusion is defined as ejaculation, although the Church in no way means this to argue that the marital act cannot continue past ejaculation) in an act open to new life. This is part of the reason (but not the only reason) that homosexual acts are disordered and sinful, because the acts themselves are closed to new life by nature of being between two members of the same sex.Why does ejaculation have to occur in the vagina? If it is because of procreation, then again, I ask, why should it matter if the couple is incapable of having children?
Now to address your question more directly, an infertile couple can still have sex that, by its nature, is open to life despite there being little or even no possibility of actual life being given through such an act. The openness to life is not defined by one’s biological ability to produce such life, but rather by the marital acts they choose to engage in. One may engage in any non-degrading, consensual, private sexual act as foreplay or “afterplay” with their spouse, but vaginal sex must occur at some point (the unitive nature of sex) and vaginal ejaculation must occur as part of sex (the procreative nature of sex).
This is also why permanently impotent men (e.g. cannot get erect, cannot penetrate, or cannot ejaculate) cannot validly marry if they have such a condition at the time of marriage, because they would be unable to engage in a procreative marital act. The same holds true for permanently impotent women (e.g. those who cannot have vaginal sex from the point of marriage or before to the end of their life for whatever physical reason), though their impotency is significantly less common and usually treatable even when it does occur (and thus not permanent).