My attention was recently called to Tibor Machan’s paper “Self-Ownership and the Lockean Proviso” (working paper version), which will be in his book The Promise of Liberty (Lexington, 2009). As noted in the Abstract, the paper argues as follows:
Locke’s defense of private property rights includes what is called a proviso–”the Lockean proviso”–and some have argued that in terms of it the right to private property can have various exceptions and it may not even be unjust to redistribute wealth that is privately owned. I argue that this cannot be right because it would imply that one’s right to life could also have various exceptions, so anyone’s life (and labor) could be subject to conscription if some would need it badly enough. Since this could amount to enslavement and involuntary servitude, it would be morally and legally unacceptable.
Other libertarian criticisms of the Lockean Proviso include Rothbard, ch. 29 of The Ethics of Liberty; Hoppe, p. 410 et pass. of The Economics and Ethics of Private Property; and de Jasay, p. 188 and 195 of Against Politics (also discussed on p. 91 in my review thereof).
See also my own critique of what I call Walter Block’s “Blockean Proviso“. As I note there, the Lockean Proviso says that you may homestead an unowned good but only if “enough and as good” is left for others–that is, if you don’t harm them by your homesteading action by making it more difficult for them to have a similar opportunity to homestead some goods of that type. Both Block and I would reject this. But the Blockean Proviso would say that you can only homestead property that is a potential means of access to other unowned resource so long as enough and as good access to the unowned resource remains available!