They inspire people who follow their precepts to angrily fight
  against some perceived establishment.   They're all products of
  the 19th century and are considered heroes in 21st century
  academia..   It's true that when people like one, they usually
  like all three. Sort of, "If you like Darwin, you'll LOVE Marx.
  If you like Marx, you'll LOVE Nietzche. And if you like
  Nietzche, well, have WE got a treat for YOU!"