What is the theme in The Monkey Wrench Gang by Edward Abbey?

The primary theme of the novel is the environmentalist beliefs of the characters, and the steps these individuals are willing to take in order to protect the environment. Hayduke as a semi-psychotic Vietnam veteran is convinced that the environment is the only thing left worth saving in the world. His actions, however, seem contrary on many levels. On one hand, Hayduke is a beer guzzling litterbug who would happily take a human life. He uses fire to destroy machinery, which in turn destroys the environment. He drains bulldozers of oil, but lets the oil seep into the ground. While his cause is just and pure, his actions are not.