I think it's right to look at this in the broader social picture.
In the late sixties things changed - MLK and Kennedy assassinated, Civil Rights Riots, Student Riots in Paris, Brian Epstein died (which changed Lennon), Lennon met Yoko, musicians stating dying, Sharon Tait slaughtered.
These things changed Western Culture. Music, Film (Easy Rider being the start), Literature, and COMICS.
I find the late sixties/early seventies a fascinating period where the (hippy?) mood changed significantly and shaped the way we look at things today.
Great thread. Neil