A Diversity Puzzle

It is an article of faith among the politically correct that ethnic stereotypes  - the humorless and  hardworking Germans, the voluble French, the reserved and  reliable English, the canny and thrifty Scots and Jews, the excitable Italians, the stolid Scandinavians, the laid back and procrastinating Hispanics, the dedicated and hardworking Japanese and Chinese, and so on - are barbarous relics without a shred of validity. Among the same people it is an article of faith that a student body or workforce comprised of people from many various ethnic groups gains strength from the different viewpoints and ways of thinking and behaving that people from different ethnic groups bring to the mix solely by virtue of belonging to those groups. It would be interesting (and probably fun) to see how a diversity peddler who was put on the spot would reconcile those two beliefs.