As Amanda Bayer and Cecilia Rouse have documented, microeconomic experiments and other research demonstrate the benefits of diversity for group deliberations and decisionmaking.
In the decade preceding the financial crisis, central banks kept interest rates at very low levels, partly due to an environment of seemingly exceptional macroeconomic stability. Another important factor was certainly the widespread opinion prevailing at that time, that monetary policy should not lean against a bubble that is building up, but intervene after a bubble has burst.