[alarge]

Are you asking about diversity of race only? Or diversity in general? The argument is that a more diverse student body creates a better educational environment for everyone - it broadens the experience. In addition to your academic studies, you learn about interacting with people who are different from you. People who think differently, reach different conclusions, even when confronted with the same data.

Racial diversity is only part of the equation. You also want gender diversity and class/income diversity - any of the major factors that shape how we view the world.