It's wrong because it violates the fundamental assumption that all people are born (or created, if you're a deist/theist) equal.
And why is that fundamental assumption important?
The majority of discrimination in the US is the soft kind because it is so incredibly hard to prove.
Um, are you saying that we have not been successful in making discrimination significantly harder than it was, say, 60 years ago?
I'm saying overt discrimination has been significantly reduced while soft discrimination has not, it may even have increased as the bigots learned what they could get away with if they just keep their mouths shut in front of non-bigots.
However, when government takes those superficial societal divisions, and puts them into law (every U.S. govt form with personal info that I've seen includes a field regarding one's race - why? - and "hispanic" is one of the options - why???)
Why? Specifically to measure if discrimination is occuring. Like the way arrest reports are required to indicate race of the arrestee and that data has shown a disproportionate number of arrests of blacks vs whites.
The remaining "privileges" these days are not at all obvious.
Unearned privileges are rarely obvious to those who posses them, that's why they get so nasty when they lose them - they don't see it as no longer getting special treatment, they see it as others getting special treatment. Witness all of the pissing and moaning about gay marriage "destroying the sanctity of marriage." It doesn't matter how it happens, those losing their place at the top will always be unhappy about it, so coddling them is not a priority.
If you raise kids to believe that artificial divisions do not matter, they won't expect special treatment when they grow up.
Yeah, well, in the best of all possible worlds, that would actually be possible. In the world most of us live in, that's a pipe dream. Quotas - which, if you actually look into it in the USA are rarely actual quotas - don't carve out different groups, they just recognize that society in general already treats members of these groups differently.