I disagree.   Some numbers to consider (from http://co.hawaii.hi.us/bigislandag/default.htm):

  •   500 acres produces  7 million pounds of guava
  • 2,700 acres produces 36 million pounds of papaya
  • less than 400 acres produces over 1 million pounds of taro, a traditional food of Pacific Islanders

This all sounds very productive to me. With over 60,000 acres of agricultural land being recently released from sugar cane production, farming just this land would require supporting about 3 people per acre to be self-sufficient on the Big Island.  Statements from John Jeavons indicate that biointensive farming would support over 10 people per acre sustainably.
One of they ke advantages of Hawaii is the temperate climate.  They only use about half of the energy per capita that is used in Texas.