Aside from earning a degree so one can find a job that will sufficiently compensate them, one of the reasons people attend college is to develop and mature as intellectuals and human beings. This is part of the reason why some colleges have distribution requirements: the hope is that students expose themselves to previously unconsidered viewpoints and become more well-rounded, empathetic people.
Generally speaking, this is a good thing: making oneself more cognizant of the struggles of others makes it easier for us to relate and sympathize with them. I think about this whenever I remember how my friends and I acted and thought when we were younger. We never did anything to be intentionally insensitive or offensive; however, our ignorance often meant we did exactly those things without realizing it.
That isn't quite what happened at Phoenix's Desert Vista High School, but it's close enough for the sake of argument. Though it is often lost, there is a difference between intentionally doing something offensive and intentionally offending. It's basically impossible to argue that those six girls (plus whoever was the photographer) did not mean to pose for the photo and post it to social media.
Unless one wants to suggest they randomly arranged themselves such that their shirts spelled out the n-word—which had a 1-in-360 chance of happening, given the two asterisks—and the photographer took the photo without noticing anything amiss, which essentially required the photographer either to have been a foreign exchange student or have taken the photo without looking. They almost certainly thought it was a joke (unless one believes they planned the stunt days in advance). Further evidence for the theory the girls thought it was a prank comes from the fact that they posted it to Snapchat. If they meant the photo to be malicious, then surely they would have posted it on a more permanent medium?
All of this isn't to absolve the high schoolers of their punishment: the fact that their photo was a practical joke doesn't mean it doesn't merit a suspension. Petitions going around calling for their expulsion—let alone the termination of the school's principal, who had nothing to do with the photo--are excessive, as is the rescission of athletic scholarships. Certainly what the girls did was ignorant and insensitive. Yet being (unintentionally) ignorant does not make one an inherently bad person; it just means one doesn't know any better. And why would they? Race isn't a problem for them, so they don't have to think about it; and they certainly aren't learning much about it in school. (To Stacey Dash: this is why Black History Month is still necessary.) Nor is this particular to those girls, that school, or even just Phoenix or Arizona: most people know precious little about America's race history because they aren't taught about it.
On a personal level, I'm correcting that by taking courses in Harvard's Department of African and African-American Studies. Such classes are optional, however; and by the time one reaches college and adulthood, many prejudices are already ingrained in the mind. If we really want to eliminate racism, we have to start talking about it more frequently--and we may have to make it more difficult to opt out of the conversation.