Homogeneity is good only if you are moving towards the optimal goal. Diversity is good to bring in new ideas which helps adjust the goal and keep the society robust against failure. Like autocracy vs democracy. If you have a benevolent godly dictator, that's perfect. But we accept that no such ideal exists, so democracy is the compromise. Diversity in the workplace exerts the same goal. It lowers efficiency, but efficiency is pointless, even counter-productive if it is towards the wrong goal.