If somebody controls all of some valuable commodity or service and no-one else knows how to produce it, that somebody is a monopolist. If I lament that his high prices are therefore immoral, do I have a case? I would say that the answer is in general "no".
Consider now the analogous case in which one man possesses very many characteristics prized by females, so that hundreds of women really would like to marry him in a gargantuan group marriage. This is of course not without precedent as harems have historically been a part of many countries' institutions. However, the man only wants one woman - who may or may not end up paying a higher "price" for having him all to herself.
The man is a monopolist for only he possesses that very combination of qualities which makes women like him so much. One could imagine that he has done something really extraordinary so that he really has no close substitutes. So why should it be OK to deplore the traditional monopolist but not the popular gentleman? As far as I can tell, it should not be OK. Perhaps the reason has to do with rights.
One has the right to do as one pleases with what one owns. Therefore, popular males have no obligation to be polygynists and monopolists have no obligation to supply more of what they can produce. Of course, this assumes rightful appropriation, so very many actual monopolies might be said to be immoral. But in my idealized case, I have trouble seeing some other plausible defence of the monogamous man, though maybe I am wrong.
With some things, the appropriation of some of it leaves less for others to enjoy, some of whom are unborn. John Locke defended private property of land as long as the appropriator leaves as much, and of as good quality, to others, which seems quite impossible on a spherical earth. But maybe one's efforts on one's land can raise the value of land nearby and produce stuff others value, which compensates the non-owners. However, if one has the right to do as one pleases with what one owns, one can also use the land as a dump.
The thinking presented in the paragraph above contradicts the defence of the monogamist. If one has an obligation to leave as much for future generations who could not help not existing yet, then one should make maximal use of one's resources now, including capacity to procreate with willing persons. But if one may do what one wants with one's property, there is of course no such obligation.
The justification for why one might have an obligation to future generations (even if one has no obligation to one's contemporaries) says that contemporaries can act now, so any resources presently up for grabs may go to them if they apply themselves. Not so for the unborn. It is right and proper to point to the tendency for individuals to use their resources optimally so that future generations are compensated, but what this blog post deals with is the moral question of why it would be wrong to fail to optimize.
Notice, however, that if people did not care about material things, nobody would challenge the landowner who refuses to do anything worthwhile with his property. It is only because people care that some say he is obliged to maximize. If people care by and large, but the landowner does not, those who care will probably get rich and either buy the land from the non-maximizer or find ways to live without his land. In this way, non-maximizers count, too.
In other words, if there are people who do not care about maximizing, should not their wishes count to those who do? This argument appears to me to win the game for natural rights.