I don't really agree with this. My company (currently 3 people) was ethnically homogeneous before I came onboard. Diversity of thought did not increase much when I was hired, even though I am ethnically different. (I studied computational science in college instead of computer science, talk about diversity). We may hire a 4'th person - a business guy who would bring a LOT of new ideas and skills to us. Ethnically he is the same as everyone else here.
Diversity of ethnicity != diversity of thought. It's a fallacy to equate the two.