Humanism's roots in modern subjectivist metaphysics

One can say at least that for humanism as a way of thinking and acting in the world that the human stands front and centre. These days, this is criticized by calling it anthropocentrism, which is not what I want to do. Instead, I first point out that there is a question concerning who the human is. This question is already different from traditional metaphysics in that it seeks a who-answer. The first metaphysics we have, Aristotle's, is an investigation of _to on haei on_, i.e. of beings AS beings, which is then given a what-answer, _ousia_ (beingness or substance) or _to ti aen einai_ (the what-it-was-ness, essence or quiddity). The AS is the hermeneutic AS that casts the mould for how beings as a whole can and must show themselves, i.e. be interpreted, in any given historical epoch.
The modern age, in which, starting with Renaissance humanism, humanism has emerged, coincides with the historical casting of human being itself AS subjectivity (a kind of whatness or quiddity). The human becomes the subjectum, i.e. 'that which underlies', which is an historical, epoch-opening eventuation. In antiquity, the subject was literally the _hypokeimenon_, which in our modern age is precisely the 'object'. So the tables have turned 180 degrees. (How come? Nobody asks these days.) In the Middle Ages, the human being was a creature, created by God, and hence also not a subject, but the ob-ject 'thrown toward' its creator, God.
From the start, the modern age is to be an epoch in which the world is to be set up in accordance with what serves humanity, i.e. the 'underlying' human subject. The world becomes that which is represented in the consciousness of a human subject, and everything in the world, including in part even other human beings themselves, becomes the object for the subject. Object and subject can never be separated. Despite this, thoughtless ways of talking do (futiley) separate object and subject, especially in the sense that there could something like objective truth over against mere 'subjective' opinion. Hence scientific method becomes crucial to purportedly guarantee some kind of objective truth by eliminating the subjective element. The sciences strive for such objective truth that, according to Popper, is open to falsification, again in line with scientific method, whose 'truth' is purportedly beyond question -- and beyond metaphysics. This is denial and self-delusion.
In such a humanistic world of subject and object (and also long before), the human has become a 'what'. Who the human is receives a what-answer such as res cogito, i.e. a cogitating thing. Relations among humans are thought AS inter-subjectivity, again without putting subjectivity itself into question.
Within the hard, 'objective' sciences, in which efficient causality reigns supreme, human freedom finds a last, cliff-hanging refuge in quantum indeterminacy, as if human freedom were somehow derivable from the indeterminacy of quantum particles such as photons, electrons, positrons, etc. etc.
If one doesn't go along with this hard, scientific objectivity, one finds refuge for the humane across the road in human ethics and values, as if these were something higher, untainted. On closer inspection, however, these 'higher values' are themselves a what, which they must be, because human being itself is conceived entirely in the third person. Especially in the general everyday exchange among human beings in the endeavour to earn a living, reified value in the shape of money, capital, wages, ground-rent, interest, profit, etc. does its job, without this veil of reification of value ever being seen through. The human subject (and economics) accepts this as the factical objectivity of the world of value-things, or rebels with an appeal to 'values' such as freedom and justice, or perhaps even compassion and friendship.
Kant, in a certain sense, presents us with the pinnacle of subjectivist metaphysics with which many a humanist and almost any enlightened politician, and many others besides, can readily identify. Kant neatly separates his Critique of Pure Reason from his Critique of Practical Reason, which amounts to separating objectivity from values in the sense of that which ought to be. Human values are to be stuck onto objectivity to make it morally humane, whereas sociology strives for so-called 'value-free objectivity' to conform with scientific method. In Kantian thinking, the world is to become more humane through an historical movement of gradual approximation to what ought to be. Kant's moral subject, however, remains a subject in the third person and hence a kind of what.
Without posing the question as to who the human is, as opposed to what the human is (e.g a needy being), freedom and justice remain empty shells, readily institutionalized. Society itself, i.e. the association of humans with one another, is thought, for instance, AS the satisfaction of needs, AS the efficient allocation of resources, AS a sustainable economy demanding a set-up that delivers for everyone. Especially in post-war Europe, where Social Democracy has been hegemonic in politics and also as an unquestioned, 'humanistic' way of thinking, justice has been degraded to the redistribution of reified value (e.g. taxes redistributed as welfare benefits) for the sake of those less well-off, thus making them clients of the welfare state. In such a way of thinking, so-called 'social justice' amounts to compulsory, state-administered charity.
However, who is the human being in all of this elaborate, partly wished-for, set-up? One imagines that all human beings on the planet exist and hence have certain inalienable rights enshrined in certain charters, etc. Political institutions have been set up to accommodate and strive for the realization of such ideals. What does it mean, however, for a human to exist? For modern science, if you're not brain-dead, then you still exist. Does today's human exist? Where is it seriously asked today, what it means to exist? It is taken for granted as a given empirical fact which is at most correct, but never true. Since we inevitably and always share a world with one another, who we are depends upon the interplay that we play out with each other, appreciating, esteeming, estimating, valuing each other (or not) -- not AS subjects of consciousness and also not AS merely factually occurring human beings.
As far as I know, no variant of humanism (and certainly no modern science, including the social sciences) poses the question as to who the human is, nor distinguishes the third-person, thingly character of human being from the first-and-second 'insubstantial' interplay between you-and-me, nor delves into the phenomenon of how a human being becomes a self through ex-sisting, i.e. standing-out, in the world, thus gaining an identity, An identity AS who you are is gained only by seizing your very own potential for existing from those identities offered by the world, especially the world of others, in the finite time-space in which you have been cast, striving, or failing to strive, to find and cast your ownmost self.
The modern age with its modern sciences, including sociology, psychology, economics, must eliminate the individual, first-person subject and also the interplay between you-and-me because they cannot be brought within scientific, controlling grasp. Empirical social science studies always require people en masse to achieve scientifically reliable and 'telling' results. These people do not exist, however.
As far as I can see, the question concerning whoness is barely on the agenda. Blindness, especially that induced by the gamut of modern sciences, rules the day. One resorts to all sorts of what answers, one makes, say, moral appeals to responsibility, one points to an urgency to address 'obvious' problems without ever coming back to simpler questions. We need first of all to learn to see, and that will take time, historical time, which is the temporal clearing we inevitably, knowingly or unknowingly, inhabit so long as we are human beings.