Note that even now not everything around us is privately owned, and most people would agree that what remains privately unowned, such as the atmosphere we breathe and the pavements we tread, should not be available for privatization. But the better part of what we need to live is, by now, private property. Why was its original privatization not a theft of what rightly should (have continued to) be held in common? (p.73, emphasis added)
For Nozick, "The crucial point is whether appropriation of an unowned object worsens the situation of others." (Anarchy, State, and Utopia, p.175) This raises two issues: 'worse' in what respect, and in comparison to what? Regarding the first issue, Cohen notes (p.80):
[E]ntitlement theorists frequently neglect the value people may place on the kind of power relations in which they stand to others, a neglect that is extraordinary in supposed libertarians professedly committed to human autonomy and the overriding importance of being in charge of one's own life.
As for the second, Nozick holds the relevant baseline to be continued unownership. His proviso ignores whether alternative ownership arrangements might have made some - or even all - better off. This "arbitrary narrowing of the options" amounts to a doctrine of "first-come, first-served" (Kymlicka, Contemporary Political Philosophy, p.117).
It would seem more plausible on both counts were the proviso to require the consent of others affected by the appropriation:
If we exclude paternalism, and emphasize autonomy, as Nozick himself does elsewhere in his theory, then presumably [others] should have a veto over appropriations which exclude [them] from the commons. (Kymlicka, p.117)
This would ensure a fairer initial distribution of resources, rather than allowing a few individuals to seize a grossly disproportionate share of natural resources to the detriment of others. Nozick denies that any harm is done, because he holds unownership to be the only relevant basis for comparison, and the disabled or talentless "would have died in a state of nature anyway." (Cohen, p.86) But as Kymlicka points out:
It is odd to say that a person who starves to death is not made worse off by Nozick's system of appropriation when there are other systems in which that person would not have died. (p.119)
Just appropriation of natural resources must fulfil the 'Lockean proviso' that others are not made worse off. This will only serve to support capitalism if one focuses on merely material well-being, and takes continued common unownership to be the only relevant alternative. But both these assumptions are unacceptable. Libertarians, of all people, should recognize the value of autonomy. But when autonomy is taken into account, it is not so clear that privatization makes no-one worse off, even compared to continued unownership. Moreover, our comparisons should also take into account the alternative systems of appropriation that could have resulted instead. Once these are considered, it seems most likely that disproportionate appropriations of natural resources will not be allowed, for they disadvantage excluded people relative to more egalitarian alternatives.
Indeed, every possible appropriation will be suboptimal for someone or other. The proviso would be overly stringent were it to rule them all out on this basis. But Nozick's proposal is far too lax, and it isn't clear what 'middle ground' a more appropriate proviso could take. Without some plausible account of what "relevant alternatives" we ought to take into consideration when assessing appropriations against the proviso, we thus lack an adequate account of initial acquisition. And without a plausible account of how property rights come into existence to begin with, the libertarian 'entitlement theory' never gets off the ground.