"If you want the best people working at your company, you should want a group with similar demographics as the customer population"

It's not the role of every single worker to deal with how the customer interfaces with the product. So what's the point in having diversity at every level?

"and if you disagree with that, you either believe there is something inherent about certain groups that makes them better or worse at these jobs,"

no.

"or you believe that there are external social biases which cause the discrepancies."

nope