Why are "descent" categories (e.g., Category:Fooian people of AAA descent) meaningless and improper. (See WP:OCEGRS).

Let's take it step by step: Our policy on non-notable intersections by ethnicity, religion, or sexual orientation (EGRS) cautions that: "Dedicated group-subject subcategories, such as Category:LGBT writers or Category:African-American musicians, should only be created where that combination is itself recognized as a distinct and unique cultural topic in its own right. If a substantial and encyclopedic head article (not just a list) cannot be written for such a category, then the category should not be created. ¶ Likewise, people should only be categorized by ethnicity or religion if this has significant bearing on their career. For instance, in sports, a Roman Catholic athlete is not treated differently from a Lutheran or Methodist. Similarly, in criminology, a person's actions are more important than their race or sexual orientation. While 'LGBT literature' is a specific genre and useful categorization, 'LGBT quantum physics' is not." So, we are told that unless there is a notable intersection between the EGRS and the topic such that a proper non-list article may be written (beware of WP:SYNTH), we ought not create or retain such a the category.

Seems straightforward and severely curtails Category:AAA Fooians type categories. But what about Category:Fooian people of AAA descent categories?

In my view they are at least as bad for both the reasons expressed in our policy and others, including the following: (a) what do Fooian people of "AAA descent" do differently than those who aren't (i.e., why is this notable - could a non-list article be written on that? why are they distinct regardless of the points below? (b) how do we objectively define how much "AAA descent" makes one eligible for inclusion in such a category? is it a One drop rule? (c) how do we objectively define how recent must that "descent" be? If you credit that our species evolved from Africa, we're all of "African descent" ultimately so this is a universal like adding categories like Category:Human beings to all biographies (d) what reliable sources tell us that each person (and, remember, we are categorizing people) meets the objective criteria above? Remember again, the biography's subject is not a reliable source as we have numbers of notable instances of people either falsifying their ancestry or ignorant of it. Moreover, realistically, only the female line of descent for most is reliable - fatherhood may or may not be with the mother's spouse or partner. (e) further erosion of concept (a) is demonstrated by the conundrum posed by children raised in the "AAA descent" (however defined) household: is WP's position that a natural child differs notably than one adopted at birth? What objective criteria does WP's position imply on the nature vs nurture debate?

Presumably if one can overcome (a) in the first instance, which I believe no one has thus far demonstrated, especially considering (d). Whatever difference attributed to this "descent" must be attenuated as the percentage of such descent (b) declines and the time (c) when the whatever environmental factors that evolved this supposed difference increases. Unless one takes the position that the merest of "AAA descent" works like a Mark of Cain that cannot be removed from generation to generation no matter where one's descendants goes assuming we can ever really know who is descended from whom - see (d). That thinking gets close to racial essentialism and clearly puts WP on the side of purely nature in the nature vs nurture. Does anyone have a reliable source for that?