In his discussion Locke's Proviso, Robert Nozick articulates some worries about interpreting the proviso as requiring the maintenance of some baseline (Nozick Anarchy, State and Utopia Part II Ch 7 Section 1). In particular, Nozick is worried about how to cash out Locke's proviso against appropriation; an appropriation is unjustified if there is not “enough and as good” left for others. If the proviso is understood as protecting agents from falling below a certain baseline, then we must confront the problem of establishing what that baseline is. Nozick, and those who follow his interpretation of Locke, abandons the baseline conception and instead adopts a Pareto-Optimal view of the Proviso. Namely, a taking is unjustified when an agent's current situation is worsened, where worsened must be evaluated in terms of opportunities created and lost, etc.
Without getting into the reasons I disagree with this interpretation of Locke's proviso, I've always been bothered the skepticism about baselines. I just don't see why the baseline needs to be given to us in the theory. It seems to make just as much sense to say that “the baseline” is a set of conditions deemed minimally tolerable. As such, the baseline will change as the affluence of the society changes. Consider current debates over socialized health care in the United States. A century ago, the most affluent nations in the world did not provide health care for anyone. After the devastation of two world wars, European nations dealt with rebuilding by socializing their economies, including health care. Now, citizens used to socialized health care consider it a right, something that they would be offended at losing. That attitude has crept into the United States, and citizens justifiably wonder why it's not possible here when it seems to work well enough over there. Of course other citizens feel differently, but many reasons for disagreement are financial in nature. In other words, they amount to worries about whether or not such a system is economically feasible. It must be feasible if it's done elsewhere and those economies are no more in collapse than ours. As the calls for health care get louder and louder, doesn't it make sense to say that the baseline has changed? The Founding Fathers might never have conceived of such a thing, but we might come to think it necessary for the continuation of our society.