There are many sense of "natural," however. Liberal values may be natural metaphysically, in that the values occur within nature. But they're unnatural in that human progress depends on a contrast between artificiality and the wilderness. Those values are unnatural in that they guide us to revolt against nature's wild qualities (mindlessness, amorality, godlessness), to replace the wilderness with an artificial, human-centered domain. In the wilderness humans count for nothing special since nature is indifferent to everything that's natural in the sense of being physical. But in our artificial refuges, we're gods (i.e. narcissistic, know-it-all consumers).