Ever since the creation of the world, the eternal power and divine nature of God, invisible though they are, have been understood and seen through the things God has made. (Romans 1:20)My assumption always is that, while the Holy Scriptures do indeed contain all that is necessary for salvation, if "there is anything at all that is morally universal" (to paraphrase Brian MacArevey), then it can be determined independently of Scripture. (I'm sure there's a good quote of St. Thomas Aquinas' to invoke at this point, but I honestly can't be bothered to look it up.) Kantian deontological ethics (and other systems of secular moral philosophy) may have its flaws, but I don’t see that those flaws are any greater from a philosophical perspective than a meta-ethic of “Whatever the Bible says, is good.” Generally, speaking, liberals and post-liberals--whether their post/liberalism be theological, political, social, or some combination thereof–-are not relativists; indeed, their--our!--post/liberalism motivates and is motivated by some very strong normative claims about human dignity.
The continuing, ongoing, and Spirit-led dialectic between scripture, tradition, reason, and experience (which is, as I have often noted here, a reflection of the perichoretic dialectic which is the Triune God) will always be allowed to override any “newly universalized viewpoint.” This, I believe, is how the Spirit moves through history, as I have already discussed at length in my essay History and Christ.