I'm curious what it is about Paul's statement (especially in light of the rest of the Bible) that makes you think he was talking about NON-procreative sex. To me it seems to coincide easily with the notion of procreative sex, without a hint of Paul suggesting otherwise.
Incidentally, they cannot do this within the Catholic sacrament of matrimony, which requires both to commit to attempt to have children and raise them in the Catholic faith.
If you're saying they may have more prominent reasons on their mind, well of course. But they cannot deny the essential elements of marriage and still validly claim to be married. Intending procreation is one of these.
Marrying for secondary reasons is morally licit, even praiseworthy, so long as it is not done at the expense of the primary reason. Ergo there is no sin in an knowlingly infertile couple marrying out of a desire to join their lives together, even if there is no prospect for having children. They are not making a conscious choice to reject children.
And finally, in the real world, I don't know if ANY couple REALLY knows whether they have the emotional maturity to be responsible parents when they get married.
Obviously, since we are all fallible human beings, no one is ever prepared to be a perfect parent. The issue is not whether a couple is 100% sure that they can handle children right away, but whether they have enough confidence in themselves to accept the responsibility should children come shortly after the exchange of vows.
If they are not willing to accept parental responsibility right away, they have no business getting married.
I think your exegesis of St. Paul is right on.
"But if they cannot control themselves, they should marry, for it is better to marry than to burn with passion."
Someone told me today that their take on it is you have to understand Paul in the context of his, and therefore the Church's, position that his calling (celibacy and priesthood) is a "higher calling" than that of marriage. He isn't denigrating people who get married, but he's stating that "sacred celibacy" (don't know chapter or verse) requires more of a person called to it (hard to disagree).
So MAYBE Paul isn't saying "if you don't have self-control, get married even if you're otherwise not emotionally ready so at least you're not fornicating," he's saying "get married when you meet a like-minded person and stay celibate until then, taking comfort in the fact that your passions won't have to burn for a lifetime."
I'll deal with it, because this is such an utter misreading of it. The passage is in 1 Corinthians 7.
The context is St. Paul extolling the virtues of perpetual continence. The statement "better to Marry than to burn with passion" refers not to couples dating each other who cannot control themselves, but people attempting to fulfill perpetual continence who find that they are not called to this work of supererogation. St. Paul says it is better for them to marry than to be burnt for sinning.
"But I say to the unmarried and to the widows: It is good for them if they so continue, even as I. But if they do not contain themselves, let them marry. For it is better to marry than to be burnt." (1 Cor. 7.8-9)
A dating couple so filled with lust that they cannot control their passions is not going to free themselves from sin by marrying - they will only heighten their sin by abusing the Sacrament. Lust is a sin regardless of whether it is inside or outside of marriage, because it is a disorder placing pleasures above right reason and good.
There is nothing to be "dealt with" in St. Paul except your misreading of his teaching. People not ready to have children are not ready to marry. Sacrmanetal Marriage is not for the supressing of the vice of fornication, but the fulfillment of virtue and the conquest of concupiscence. The power of creating children and the duties they entail give one an appreciation of the consequences of giving in to lust and comitting oneself to a sexual relation one is not prepared for all the possible consequences of.
Sex between married people is for two purposes - the conception of children and the growth of marital love in the Sacramental grace. The supression of lust does not enter into it at all. Marriage was created in the Garden of Eden when there was no lust and already had all its necessary characteristics at that time, other than the bestowing of grace, which was added when Christ came an sacramentalized our life.