The blessings of diversity: Only in this age could people get away with claiming that diversity is a crucial asset to society's wellbeing. I gathered data on 82 countries from various sources (e.g., World Factbook) in order to examine the correlates of ethnic heterogeneity. Here are the Pearson correlation coefficients:
Correlations with an index of ethnic heterogeneity
Social welfare expenditures (health and education as % of GDP) -.30*
Income inequality (GINI coefficient) .22*
Per capita GDP -.36*
Male homicide victimization rate .45*
Female homicide victimization rate .37*
* p < .05, one-tail test
In case you're not into statistics, the results indicate that countries with lots of ethnic diversity tend to have governments that spend less on education and health; they are poorer and characterized by greater inequality; and they experience more violence. The larger the absolute value of the correlation, the stronger the connection: the inequality correlation is weak, the male homicide one is moderate.
Conservatives might like less government spending and not care too much about inequality, so it is liberals who should be most concerned about diversity.
Now, I can't claim that the correlations prove that ethnic diversity is causing all these bad things, but I can at least say that they tend to go together: where you see lots of different kinds of people, you often see bad social conditions.
These data were originally used for other projects, so it's not like I cherry picked indicators that would make diversity look bad. I do know that I have never randomly looked at correlations and found that heterogeneity is related to a list of positive social indicators.
Multiculturalists love to blow gas about how great it is to have a real mix of people, but I am still waiting for some demonstrations of it.