Cass Sunstein in The Chronicle of Higher Education:
“When people end up in enclaves of like-minded people, they usually move toward a more extreme point in the direction to which the group's members were originally inclined. Enclave extremism is a special case of the broader phenomenon of group polarization, which extends well beyond politics and occurs as groups adopt a more extreme version of whatever view is antecedently favored by their members.”
Read it all, with particular attention to the "Colorado experiment."
Hat tip, Arts and Letters Daily.