On the one hand, the liberal acknowledges the fact of "reasonable pluralism": there are many systems of belief (and values, etc.), each equally compatible with observation, and thus none deserving of privileged status. Yet, given this pluralism, the liberal may not appeal to any notion of natural rights in his argumentation. For, the notion of natural rights depends upon superstition, and is thus particular to a given belief system (and thus cannot provide an adequate basis for an argument directed toward a pluralistic audience). The liberal thus cannot begin his argument from any vantage which assigns man a privileged status.
On the other hand, the liberal is dedicated to preserving this pluralism and, as such, must provide a justification for it somehow. The liberal, by definition, advocates a political system which protects the individual's freedom to belief systems, behavioral patterns, value judgments, and priorities of his choosing. Yet without natural rights, without endorsing a particular belief system, what foundation remains for defending this diversity?
How can the liberal move from the fact of pluralism to a normative mandate for its preservation? Between this Scylla and Charybdis the honest liberal must somehow navigate a delicate course.