values and principles

I am wondering why the NASW Code of Ethics derives principles from values instead of the other way around? Etymologically and, I think, in common usage, principles by definition come first (in principio creavit; in principio erat verbum, etc.).

Logic has a core principle--both p and not-p cannot be true at the same time (or something like that). Without that principle you cannot do logic--other things perhaps, mysticism, poetry, Zen, etc., but not logic. In ethics the core principle is, I think, that people (do or should or think they should) do good and avoid evil. Without such a core principle, ethics becomes something else--psychology or neurology or something else.

Values (if the term is meaningful) can be derived from principles, but not the other way round. If this is wrong and the NASW approach is right, where do values come from? Are they only matters of agreement or consensus among a group of people that could equally well be the opposite of what they are? Just wondering.

You might say that in NASW’s usage, values reflect the preferences of an individual or a group, while principles, as rules, are more concrete and are used to guide behavior. One could say that values are concepts and principles are the operational definition of those values. Principles here are not fundamental laws or truths or postulates, but rules of behavior. This makes sense of what the Code does.

The problem for me, then, is to understand what anchors those value preferences. Do they have any basis in the way we humans are or what in reality makes for the well-being of individuals and communities, or are they just tastes, like a preference for vanilla over strawberry ice cream?

Are Satanists and social workers just people with different moral tastes, with no way to determine which flavor is to be preferred except in terms of some other, no less arbitrary set of preferences?

Or must such preferences be rooted in some intrinsic or absolute good? So exercise may be valued because it contributes to health as an empirical fact, but that makes sense as a value only if health is good in an absolute sense.