The rioting, looting, arson, and vandalism that happened here this week might have horrified people across the country, watching it unfold on 24-hour news channels and Facebook feeds. But no one in this city should have been surprised. Much of Baltimore has long been a tinderbox of crushing poverty, pervasive violence, racism, and stark socioeconomic divides. It was only a matter of time. For the dozen or so colleges that occupy Baltimore, the city has been a laboratory, a challenge, a stigma. The unrest of the past few days — spurred by the death of a black man who was severely injured while in police custody — is leading some of the city’s colleges and scholars to ask new questions about their role here.