How Douglas Adams started the series:

     It's like this:  the central character, Arthur Dent, has his home
 destroyed, by the forces of order.    And planet Earth gets bulldozed
     So, Earth being the home planet, the whole thing gets kicked off by a
 sense of the loss of home.  Like that.

(No pun intended, by me anyway: ) 'Loss of home' leads to a sort of alienation. It propels the series, to a great extent.
That's about it.

(You mean you were expecting a long, serious, scholarly spiel? like mentioning the eco-fragility consciousness thing subequent to Rachel Carson's 'Silent Spring', Jungian vs. Freudian, etc., etc. - ? You looked in the wrong place, that's all; read the books themselves, if you want a big block of Meaningful Content.)

(C) R.H., Sept. 12, 1998.

[P.S.: If you want something ponderous to read, lengthy and intellectual, then my 'Short Guide [etc.]' is certainly not for you.]