Frustration with censorship and editorial interference led to a group of Pilote cartoonists to found the adults-only L'Écho des savanes in 1972. Adult-oriented and experimental comics flourished in the 1970s, such as in the experimental science fiction of Mœbius and others in Métal hurlant, even mainstream publishers took to publishing prestige-format adult comics.

Pilote cartoonists were upset with censorship and what?