Actually, cosmological physics (especially the Second Law of Thermodynamics) and mathematics would have a lot to say about the potential of immortality. One might be able to prove mathematically that only a finite number of souls could enjoy immortality, it seems to me. The concept of entropy would explain why reproduction (procreation) is necessary.
The Washington Post has a major story on Mormon social values (by Michelle Boorstein) Jan. 12, here. A larger percentage of Mormons than of the general population believe that being a successful parent is the most important thing one can do and believe that having a good marriage is mandatory. Note that the moral belief centers on the idea that a person is required to perform a pre-existing obligation (getting and staying married and raising children as an oblication), rather than follow through on a choice already made (having sexual intercourse that happens to result in children), the latter of which has become the "libertarian" idea of personal responsibility.
The Pew Research Center has a report Jan. 12, 2012, "Mormons in America: Certain in Their Beliefs, Uncertain of Their Place in Society", here.