there is no intrinsic value, and therefore valuing is required as a finite process among other, succeptible to context and change, and because of that capable of progressing.
So you conclude "there may be value depending on the context"; if this is so, then only one who has educated oneself about
the entire diversity of contexts and the whole of history can say that he has the correct "finite process" for valuation. So this path to knowledge obviously involves learning about the other worlds and those
rational beings of a different and higher kind. You also would eventually have to realize that the world in which we live is not the only one in which we shall live or have lived, and that there are contexts presently unknown to you. This very line of reasoning denies humanism, and it is a problem for the nihilist because according to secular scholars, "all
rational atheists are humanists" (unless you are some oddball French philosopher from the 20th century). The nihilist needs a wide diversity of contexts in order to have a complete glimpse into the valuation problem, therefore any educated discussion of these contexts will turn to
the subject of extraterrestrials, etheric beings, and the like.
Succeptible, not reduced to, there is absolute knowledge, you don't need to know irrelevant contexts and you don't need the knowledge of the whole to determine which are irrelevant, you only need knowledge of knowledge to do that. Perhaps we should keep the churches and teach epistemology in them. The line of thinking you describe does not deny humanism, not in philosophy at least, it does go against the standard humanism of human self-imporatance most commonly found among historians and the touchy-feely humanism of the social sciences.
You assume valuation is a relative measure that it depends only on empirical knowledge, but we don't need to compare a human to a galactic hive-mind in order to compare it to a plant, and we don't need any particular empirical knowledge in order to determine the idea of good.
I think that your version of nihilism is nothing new;
In place of the old morality, we will get the new morality-one that's more relevant-namely that "nothing is real except our world of desires and passions," as Friedrich Nietzsche phrased it in his book Beyond Good and Evil. Formally, this philosophy is not called pluralism, but secular humanism. The problem Christians have with secular humanism is not that it is truly pluralistic, but that it subjects man to the sentimentality and enthusiasms of the moment. Indeed, history has shown that secular humanism - the view that man is the sole judge of the world, including morality, the shape of society, and the value of the individual - is very bad for humanity.
The assumption that is required in your argument is that human knowledge of value can progress, but this is dependent on
humanism, the idea that man is the sole judge of all things.
How can you say that man's knowledge of value
can progress unless man himself is the judge of that progress?
Nietzsche was not a nihilist, he was one of its greatest opponents, as he saw it as a mere reaction to theism (as is mostly the case, but as I claim not necessarily so), and he believed that there is a third option (one that leads through nihilsim and overcomes it), but he was speaking of moral nihilism, and the will to nothingness of a disilussioned culture where their value framework had lost its center (the death of god).
The idea of progress has nothing to do with the idea of man being the judge of all things, but a very similar one, that rational beings are the judges of all things, this however is very unproblematic as it is a mere tautology, to be a rational being means to be a being that can judge. Progress is just another idea of value, what is required is knowledge of one idea alone, the idea of good. This knowledge is not a progression, we either have the knowledge of the idea or we don't, and the concept of progress is merely an application of it. What you're getting at is how can we be certain of our knowledge of progress? By being certain in our knowledge of idea of good. And how to be certain in the knowledge of idea of goood? You have to deduce it a priori, much like a mathematical proof, without its convience of formalization.
To take values as fixed, therefore only blocks the potential progress of values and robs them of their rational basis, that they always possess in some form. It doesn't even mean there isn't an objective basis of values, just that they aren't inherent to mere objectivity itself. As an analogy, we can take mathematics, that has an objective basis, yet isn't inherent in things themselves, but has to be created in order to describe them.
It is good that you bring up the rational basis of values in the context of objectivity; one philosopher has said:
Thinking is mans only basic virtue, from which all the others proceed. And his basic vice, the source of all his evils, is that nameless act which all of you practice, but struggle never to admit: the act of blanking out, the willful suspension of ones consciousness, the refusal to thinknot blindness, but the refusal to see; not ignorance, but the refusal to know. It is the act of unfocusing your mind and inducing an inner fog to escape the responsibility of judgmenton the unstated premise that a thing will not exist if only you refuse to identify it, that A will not be A so long as you do not pronounce the verdict It is. Non-thinking is an act of annihilation, a wish to negate existence, an attempt to wipe out reality. But existence exists; reality is not to be wiped out, it will merely wipe out the wiper. By refusing to say It is, you are refusing to say I am. By suspending your judgment, you are negating your person. When a man declares: Who am I to know? he is declaring: Who am I to live?
Since values have a rational basis, it is sensible to ground our highest virtue in thinking, and the highest evil would be to refuse to know about other contexts of knowledge and values; therefore, only a sufficiently diverse education can allow the potential for the progress of values.
This philosophers says; thinking is overhyped. Anyone can think, some can even think very well, but to know is a thing something completely different. Virtues are neat, but they are empirical properties determined as good only on the basis of a before constructed idea of good that is applied to some properties, if you only have ethics based on virtues it is completely contextual and is therefore merely a thing of common-sense morals not pure ethics. In a land of cowards, cowardice is a virtue, etc.
PS: perhaps you'll be interested in this project of Formal Theology:
https://github.com/FormalTheology/GoedelGod it detected a flaw in Gödel's ontological argument.