Steve: yes, you are right.
But, clearly Thornley had some idea for the book, and felt that Oswald fit the kind of
person he wanted to write about.
He said that "I was not so interested in explaining Lee Harvey Oswald to myself or anybody else, as I was in explaining that particular phenomenon of
disillusionment with the United States after serving in the Marine Corps overseas in a peacetime capacity; thus the title: The Idle Warriors."
But, yes, then he says: "Since Oswald inspired the book, I did base a good deal of it as a matter of convenience on his personality and his ideas."