“Diversity is our strength” is an Orwellian lie, and any rational, sane person, even a left-wing person, should be capable of seeing it at this point.
The evidence that diversity is catastrophic has been available for a long time, and some of the best research comes from the work of Robert Putnam. Notably, Putnam is a multiculturalist liberal, and he was so shocked by his research findings he delayed publishing them for years on end.
See also the following studies here:
(1) Wickes, Rebecca, Zahnow, Renee, White, Gentry and Lorraine Mazerolle. 2014. “Ethnic Diversity and its Impact on Community Social Cohesion and Neighborly Exchange,” Journal of Urban Affairs 36.1: 51–78.Wickes et al. (2014) seems generally to confirm Putnam.
(2) Sturgis, Patrick, Brunton-Smith, Ian, Kuha, Jouni and Jonathan Jackson. 2014. “Ethnic Diversity, Segregation and the Social Cohesion of Neighbourhoods in London,” Ethnic and Racial Studies 37.8: 1286–1309.
Sturgis et al. (2014) has curious findings that seem to indicate that positive attitudes to diversity decrease with a person’s age, and ethnic self-segregation actually makes separate communities more cohesive, which utterly refutes the Cult of Diversity belief that mixing up people of different racial, ethnic and religious backgrounds makes them happier or their communities more successful.