So Asian's are 5% of the US population [1] but make up 20% of the admitted applicants [2]. While African American's, representing 13% of the country [1] and a shameful legacy of mistreatment make up 12% of admitted applicants [2].
The problem is that admissions isn't based solely on your capabilities as a student at the time of application, but also on your potential to grow. Asian's tend to be fairly successful in the US (especially 2nd and 3rd generations) [wish I could find stats for this right now], if you start in a good environment with two intelligent well-meaning parents a 780 in math is impressive, if you're the son of a single mother with a father in jail and 3 younger siblings you share responsibilities for that 520 in math looks spectacular.
If I ever see Asian's in this being denied social mobility I'll raise torches and pitchforks, but in this scenario Harvard is a limited resource that provides immense social mobility for students from the lower echelons of society, if admissions were rooted solely in test scores and grades then these students with potential, but not the resources from birth, will be denied a chance to benefit from a prestigious education.
[1] http://quickfacts.census.gov/qfd/states/00000.html
[2] https://college.harvard.edu/admissions/admissions-statistics
edit: I appreciate people's rights to disagree, but I find it frustrating that the preference has been to downvote this rather than engage in meaningful dialogue.