The less measurable your admissions criteria, the more subconscious bias seeps into your decision making process. You can not extricate the perverse stereotypes that exist in society when making a decision whether a candidate is "diverse" or "well-rounded".

There have been numerous studies showing that whites favor meritocratic admission criteria, but reverse their position when shown the high percentage of Asian admits (e.g. http://www.jstor.org/discover/10.1086/670664?uid=2&uid=4&sid...). Indeed the data also shows that white admissions are barely affected in comparison to Asians (e.g. see the MCAT admissions data linked elsewhere in this thread).

It seems to me that the shroud of "diversity" is being used to preserve the existing white power structure in elite universities, especially with the prevalence of legacy admits.

Anyone who has designed a system knows that you can tweak variables to get your desired result and then tautologically justify your decisions post-hoc.