The issue of how whiteness is socially and legally constructed and maintained is incredibly complex and fascinating (at least I find it fascinating) but probably beyond the limits of this thread, as meandering as it's already been.
Maintained? It seems to me that what's maintaining this skin colour preoccupation in the USA, is all Amercian's and not just the white ones either
The most basic explanation is that the US has a huge number of Spanish-speaking/Hispanic immigrants (from either Mexico, or countries in central or South America) who historically and currently suffer a great deal of oppression and racial discrimination.
Where does the "Hispanic" label come from? Can't people just be Mexican or Cuban or whatever?
"Whiteness" is strictly controlled in the US, both legally and culturally (why they have things like the One Drop law,
Have?
how Irish people weren't considered white,
Do you have any sources for this please? I'd like to look into this further
and why the US Supreme Court has heard cases to decide whether a person - and many of these cases have been Hispanic people - is legally white or not.)
For what purpose. Why does the SC do this?
There are relatively few people immigrating from Spain to the US, so in America the assumption is that anyone who speaks Spanish as their first language is Hispanic and from a country in the Americas.
So it's parochial ignorance on their part?
The average American is not going to see a dark-haired person speaking Spanish and assume she might be white European from Spain because that's just a level of subtlety and nuance that most people don't go into.
Maybe now, if any good comes from it, they will appreciate a world outside the USA identity bubble. Hopefully