>Every study done on it has proven that diversity increases team productivity
Which studies?
They don't say that, exactly.
http://www.academia.edu/887990/The_effects_of_team_diversity...
Over the past few decades,a great deal of research has been conducted to examine the complexrelationship between team diversity and team outcomes. However,the impact of team diversity onteam outcomes and moderating variables potentially affecting this relationship are still not fullyanswered with mixed findings in the literature. These research issues were,therefore,addressed byquantitatively reviewing extant work and provided estimates of the relationship between team diver-sity and team outcomes. In particular,the effects of task-related and bio-demographic diversity at the group-level were meta-analyzed to test the hypothesis of synergistic performance resulting fromdiverse employee teams. Support was found for the positive impact of task-related diversity on team performance although bio-demographic diversity was not significantly related to team perfor-mance. Similarly,no discernible effect of team diversity was found on social integration. The impli-cations of the review for future research and practices are also discussed.
http://www.palgrave-journals.com/jibs/journal/v41/n4/abs/jib...
Previous research on the role of cultural diversity in teams is equivocal, suggesting that cultural diversity's effect on teams is mediated by specific team processes, and moderated by contextual variables. To reconcile conflicting perspectives and past results, we propose that cultural diversity affects teams through process losses and gains associated with increased divergence and decreased convergence. We examine whether the level (surface-level vs deep-level) and type (cross-national vs intra-national) of cultural diversity affect these processes differently. We hypothesize that task complexity and structural aspects of the team, such as team size, team tenure, and team dispersion, moderate the effects of cultural diversity on teams. We test the hypotheses with a meta-analysis of 108 empirical studies on processes and performance in 10,632 teams. Results suggest that cultural diversity leads to process losses through task conflict and decreased social integration, but to process gains through increased creativity and satisfaction. The effects are almost identical for both levels and types of cultural diversity. Moderator analyses reveal that the effects of cultural diversity vary, depending on contextual influences, as well as on research design and sample characteristics. We propose an agenda for future research, and identify implications for managers.
That being said, I still don't advocate a monoculture environment, if not for one reason, it isn't the right thing to do to discriminate.