In the US it is no longer politically correct to "discriminate" on the basis of race, which is great.

Yet racism continues to be deeply rooted in the "standard American mindset", as betrayed by the "race" field in forms.  To most Americans, it seems mankind is still neatly divided into five "races", with no room for qualifications or even gradations. In particular, the children of "black" + "white" parents are still "black".  

Funny thing is that Americans do not seem to realize that such views themselves are racism.  To them, it is just common sense logic. To them, the "one drop rule" is not something to be questioned; it is the dictionary definition of the word "black".

No, sorry: "race" is not a scientific concept.  All the "scientific racism" theories that started in the 18th century and continue to this day are a big load of shit -- a conscious or unconscious attemmpt to justify colonialism, slavery, discrimination and persecution.  Darwin's Origin of the Species is totally misapplied.  Mankind is just one species; its populations have become separated only very recently in evolutionary terms, and genetic mixing is still strong -- even among social groups that try hard to remain genetically isolated.

Humans in isolation are not racist.  Children are not racist.  Many "savage" tribes, while strongly "nationalistic", are not racist, and often practice exogamic (inter-tribal) marriages as a rule.  Racial segregation is always a social phenomenon, imposed by society whenever two or more groups of people are competing for power or resources.  Biological differences, liek skin color, are then only a pretext -- a convenient label used by oppressors to keep the oppressed in teir place and deny them whatever is the real object of dispute,