There are several problems with the Unfulfilled Plan of Totally Pure-Virgin Man.
1. The text which most nearly concerns the issue--Genesis--says nothing about it. One can talk about the Unfulfilled Plan of Totally Pure-Virgin Man at very great length only because one argues ab silentio, but argumentum ab silentio is a dead-end.
2. What the text does say about it is unambiguous. Even St. Augustine, everyone's favorite (nearly?) ex-Manichee, supposed that procreation was a plan for the peopling of Paradise. In order to support the Unfulfilled Plan of the Totally Pure-Virgin Man one must radically twist the texts one is purporting to explain--a habit not unknown to the Gnostics.
3. The Unfulfilled Plan of Totally Pure-Virgin Man raises more questions than the common sense view that God intended man to multiply (intransitively and transitively). Would the Totally Pure-Virgin Man also have needed a source of strength meet for him? Would he have remained the only human creature in Paradise or would he have multiplied asexually? (The view expressed elsewhere that procreation was necessary only to simply go through the numbers needed for the Messiah raises too many questions as well.)
4. The value of the argumentum ab silentio is that even if it tells nothing about the issue at hand, it says plenty about one's assumptions. The real value (to certain parties) of the Totally Pure-Virgin Man argument is that it succeeds in denigrating marriage by casting aspersions upon the sexual aspect without overtly saying that matter is evil. So, one is able to say that sex is evil, marriage is provisionally good, and totally pure-virginity is better! This account even gives something to marriage that no other sacrament has: an etiology explaining not the wounds healed but the medicine itself!
5. In general I think it would be very wise for us to remember that dualism in one shape or another has haunted the church from the age of the apostles to our own. We are most certainly not immune to the Manichean temptation that has felled so many trees with deeper roots and healthier sap than ours! When one keeps hearing rumblings about how evil marital sex is, or about how marriage, unlike monasticism (!), is contaminated by desire, etc., it is best to reread the anti-Gnostic fathers and scour Plato, Plotinus, the Nag Hammadi Corpus etc. in order to verify whose side one is on.