Scripture informs us that marriage has two purposes: unitive (that is, a physical and spiritual union - "the two become one flesh") and procreative (that is, having children - "be fruitful and multiply").
Not every marriage can fulfill both purposes, but it must fulfill at least one purpose - and since the unitive purpose undergirds the procreative purpose, the unitive is the minimum standard for contracting a valid marriage. If a relationship is neither unitive nor procreative, then it is not a marriage relationship but something else.
Another issue: impotence and infertility are two different things.
An impotent man may be fertile: i.e. he may be able to produce sperm but unable to have an erection. Only men can be impotent, by the nature of human sexuality.
A potent man can be infertile: i.e. he may be able to have an erection but unable to produce viable sperm.
A potent man is able to pursue the unitive purpose of marriage by having natural intercourse. An impotent man is unable to pursue either purpose of marriage because he is unable to have natural intercourse and unable to engage in natural procreation.
The larger picture: human beings are composite beings - they are composed of body and soul. Therefore marital union is both physical and spiritual and requires both physical union and spiritual union.
If marriage is purely based on personal affection and lacks the necessary physical component then marriage is redefined as an affective relationship between any two persons - not a physical union of a man and a woman.
There is a reason why marriage is falling apart in the West: it is being redefined as purely an emotional bond between any two people.
Hence "open" marriages. Hence "starter" marriages. Hence "gay" marriages.
“Not every marriage can fulfill both purposes, but it must fulfill at least one purpose...A potent man can be infertile: i.e. he may be able to have an erection but unable to produce viable sperm.”
That’s interesting. I wasn’t familiar with this aspect of Catholic teaching. Just curious, though — what is the barrier to gay marriage then? I always thought the problem was that it wasn’t procreative. However, it could certainly be argued to be unitive. If it’s the erection you’re after, aren’t two erections better than one?
The original intention of woman's creation was not for reproduction but rather companionship. Read Genesis 2 Reproduction came after the curse. Placing this burden upon men and women as an absolute is as ridiculous as having them pluck out their eyes if it causes them to sin. Does the church require that also? No!
The reason marriage is falling apart in the west is because the blasted government under LBJ created the great society. Men were going around fathering children not being responsible for them. Taking care of ones own by society was abandoned. Let the government do it. It is a moral decline and many a child was born because of it out of wedlock. So the idea that sex cures it all even in marriage is RIDICLOUS! Reproduction is but a small part of overall marriage it is a blessing if it happens. It's important but is not the sole purpose of marriage & why man and women are united. That was not the origional intention.