Baltimore's Enoch Pratt Free Library won some national recognition this month, making Reader's Digest's list of the 10 ----nicest places---- in America. If Baltimoreans spent even more time in the Pratt branches -- and, even better, if people from the suburbs joined them there -- we might have a more civil, less polarized country. That's an argument sociologist Eric Klinenberg has been pushing -- invest in the country's ----social infrastructure,---- he says, to increase the opportunities for human interaction and the possibilities for a healthier, less isolated and angry society. Klinenberg, who visited Johns Hopkins University this week, is the author of ----Palaces for the People: How Social Infrastructure Can Help Fight Inequality, Polarization, and the Decline of Civic Life.---- He is professor of sociology at New York University.