There are lots of good, bleeding-heart reasons to value diversity, to see it as a noble end in and of itself. But there are some very practical reasons to seek it out, too, as a new article in Perspective on Psychological Science points out.
The evidence on group diversity has been mixed overall, the researchers point out. They write: "More than half a century of research evidence has produced few straightforward or consistent characterizations of diversity’s influence on group process and performance, with some studies revealing beneficial effects and others documenting downsides." Among the downsides is the fact that it's harder to achieve group cohesion in heterogeneous groups than in homogeneous ones — humans have a tendency toward "homophily," or being attracted to those who are like us.
But there are group situations in which just a bit of friction can be beneficial. The researchers cite one experiment, for example, in which participants "were assigned to either a homogeneous or diverse" and then asked to solve a murder mystery:
In diverse groups, the confidence levels individuals reported regarding their group’s performance corresponded with how well their group actually performed (i.e., diverse groups that identified the correct murder suspect reported higher levels of confidence than diverse groups who did not). Individuals in homogeneous groups, by contrast, tended to report high levels of confidence irrespective of how their group performed. In short, homogeneous groups were actually further than diverse groups from an objective index of accuracy.
In another experiment (PDF), "[p]articipants were randomly assigned to all-White or racially diverse juries and asked to deliberate over the same trial":
Results revealed that homogeneous juries made more factually inaccurate statements and considered a narrower range of information when discussing a trial than did racially diverse juries... This result may have been at least partially due to an avoidance of disagreement by the homogeneous groups, which undermined the adaptive jury behaviors of information sharing and consideration of relevant characteristics. Moreover, evidence from other domains offers one reason why these effects may occur. When people are prompted to think about social category differences, as they are in diverse groups, they are more likely to step outside their own perspective and less likely to instinctively impute their own knowledge onto others... The lack of this social prompt in homogeneous groups may thus help explain why individuals’ subjective responses in these settings tend to be less objective and more narrowly construed.
Diversity, in other words, nudges you out of your comfort zone in a good way. It provokes different sorts of discussions and debates and makes it easier to resist the worst consequences of groupthink. Even if diversity is a tough thing to achieve, this is one of its extremely valuable benefits.