Click on smutty comics to enlarge.
It is flat-out impossible to re-create the socio-cultural environment of the USA when Crumb's underground comic work flourished. If you made it your Life Mission to be Banned & Busted and tarred & feathered, you couldn't have shocked America more than Robert Crumb did.
(His earliest work was for American Greeting Cards, funny novelty birthday cards you could send to your Aunt Lillian.)
But he had greater ambitions, and right about then Underground Comics were born -- comic books which proudly did not carry the Seal of Approval of the Comics Code, the comic book industry's self-censorship set of taboos. (No artistically exaggerated female breasts is one taboo I remember; there were a few dozen taboos in the Comics Code. Crumb certainly liked to exaggerate breasts, but he was particularly enthused with exaggerated -- with epic -- female buttocks.)
Crumb -- and in music, Frank Zappa -- embodied a demand (already promised by the First Amendment of the U.S. Constitution) for artistic and political freedom.
Artistically the wildly unpopular Vietnam War poured kerosene on the urge to piss on rules and laws and norms. Suddenly nothing was sacred. We were barbecuing every Sacred Cow we could find, and many of the chefs were grilling in the nude. There were Rumors that America had something called Freedom, and artists, musicians and pornographers set out to find some of it.
In 1964, a censorship case reached the U.S. Supreme Court, and Associate Justice Potter Stewart wrote that he could not define hard-core pornography, "but I know it when I see it." (The film was Louis Malle's 1958 "Les Amants"; a Cleveland USA theater owner was arrested for publicly displaying obscene materials.)