Nick Phillips:

Intellectual diversity addresses a fundamental problem in human cognition: we seek out information that confirms the views we already have. As Jonathan Haidt has argued, this instinct is well-adapted to creating intra-group solidarity, which is useful when competing for power with other groups. But if the goal is to seek the truth, it’s poison. If everyone in your group shares the same biases, that group will block new information that doesn’t conform to those biases. Since no one is right 100 percent of the time, this dynamic guarantees that falsehoods will persist. 

One solution is to attempt to purge individuals of their biases. But cognitive psychologists don’t yet understand how to do this. The only method that reliably solves the confirmation bias problem is to create groups made up of individuals with different biases. In such an environment, countervailing biases checks one another, prodding at weak points and raising questions a colleague didn’t think to ask. This dynamic is highly adapted to truth-seeking, because it forces every person to justify their biases on grounds other than tribalism.

(See also this 2009 article on “debiasing.”)