You're right preferring to be with your own is entirely natural. Diversity always causes conflict and tension.
journals.plos.org/plosone/article?id=10.1371/journal.pone.0095660
“Our analysis shows that peace does not depend on integrated coexistence, but rather on well defined topographical and political boundaries separating groups, allowing for partial autonomy within a single country. “
bjp.rcpsych.org/content/201/4/282.abstract?etoc
“For every ten percentage point reduction in own-group density, the relative odds of reporting psychotic experiences increased 1.07 times (95% CI 1.01–1.14, P = 0.03 (trend)) for the total minority ethnic sample. In general, people living in areas of lower own-group density experienced greater social adversity that was in turn associated with reporting psychotic experiences.”
“His conclusion based on over 40 cases and 30,000 people within the United States is that, other things being equal, more diversity in a community is associated with less trust both between and within ethnic groups.”
en.wikipedia.org/wiki/Robert_D._Putnam#Diversity_and_trust_within_communities
“We show that ethnic diversity or fractionalization and values diversity are distinct and while the former has a negative effect on innovation, the latter contributes positively. However, countries are bound to have both types of diversity. We find that countries that are ethnically homogenous but diverse in values orientation are the best innovators.”
tandfonline.com/doi/abs/10.1080/13504851.2015.1130785
Alienation, increased violence, isolation, destruction of community and loss of intermediate institutions, reduced civic participation and isolation from the aggregate social structure, psychosis, reduction of innovation. Humans are fundamentally a communal, not an individualist species and diversity destroys connection and solidarity. It's a communal pollutant.