Grapes of Wrath and Steinbeck philosophy?

[RaNdOm]

How does steinbeck show the belief of that humans are morally responsible for the environment in the "Grapes of Wrath"?

[pupcake]

Because it was misuse of the land by humans that caused the dust bowl. Humans were also to blame for the depression. They broke it, they should fix it.

[hurtin']

With the Joads as a focal point, S. shows how families living by their own resources are often confronted with drought and depression, and with no resources in reserve, are dislocated to search for a new start. Having their home flattened by the banker's bulldozer only begins to demonstrate the callous attitude of people who control the economy. They find aid only with others who are similarly impacted, and share what they can; 'making do' in spite of adversity.
Lesser people are ground down by larger, impersonal concerns, typified by the townspeople and cops who harass them to keep moving. Any attempt to resist for the sake of human dignity and respect is fiercely opposed, contributing to their desperation.
In fact, this is a recurrent theme in American history; the "Dust Bowl" was only the most outstanding example.