Not OP, but I think they refer to Putnam's work on the negative effects of diversity on social cohesion. https://en.wikipedia.org/wiki/Robert_D._Putnam#Diversi

Not OP, but I think they refer to Putnam's work on the negative effects of diversity on social cohesion. https://en.wikipedia.org/wiki/Robert_D._Putnam#Diversity_and_trust_within_communities https://en.wikipedia.org/wiki/Robert_D._Putnam#Diversity_and...