If diabetics can't work it would interesting to know how Arthur Ashe and Billy Jean King both won Wimbledon, Scott Coleman swam the Channel, Joe Frazier became the undisputed World Heavyweight Boxing Champion and Wasim Akram represented Pakistan in over 100 Test matches!
Also, according to that theory, we shouldn't have seen Jimmy Cagney, Mae West, Jackie Gleason or Halle Berry appearing in any movies! We'd have also missed out on the music of James Brown, Tony Bennett, Johnny Cash, Ella Fitzgerald, Meat Loaf, Dizzie Gillespie, Elvis Presley and Luther Vandross (while not being able to see any musicals written by Andrew Lloyd Webber either).
Technology might have been slowed down as well, if Thomas Edison hadn't invented the light bulb and the phonograph.
Tell your friend's partner that if Gary Mabbutt could play football for England, she can stack shelves in Tesco ;-)
Chris