At first blush, these critics have a superficial case to make. Earth's most recent colony, Lakkdarol, is a frontier village dependent upon a long lifeline to civilization. The Martian landscape does summon images similar to the deserts around Tombstone and the prairies of the Great Plains. A conflict exists between the townspeople and a brown skinned indigenous savage, which prompts the traveling Northwest Smith to intervene. Add rayguns, leather, and a line in the sand spot reminiscent of the Alamo, and it is easy to leap to the conclusion. However, closer examinations of western tropes, such as those found in The Six-Gun Mystique Sequel, by John G. Cawelti, reveal the flaws in the space western conclusion.
In a Western, when there is conflict between the town and the savage (either outlaw or alien), the savage threatens the town's way of life, and the hero is required to settle the conflict. However, it is Shambleau who is threatened by the town, and Northwest Smith needs rescue from another. She does represent a potential threat, but the townies showed that they could drive her off. Northwest Smith's intervention does not settle the conflict between the town and the Gorgon, rather he interferes with their attempts to rid the town of a monster. Rather than focusing on how Shambleau affects the life of the townspeople, "Shambleau" is about the seduction and destruction of Northwest Smith, conveniently averted by Yarol. The confrontation between the townsmen and Smith serves to set the hook of Northwest's attraction to Shambleau, not to stage further conflict between Shambleau and the town.
The elements for a western might be present, but they are not used in the same way as a western. Just as beef and potatoes can be turned into either steak with a baked potato or stew, the elements instead are used to tell another type of story with Shambleau.
Instead of an "ur-Shambleau" western, C. L. Moore stated her inspiration for Shambleau came from a poem, probably written by Victorian poet William Morris,
The red, running figure in the poem had been a young witch pursued by soldiers and townspeople in some medieval village. In my story they had perfectly sensible reasons for killing her as soon as possible.
Moore, C.L.. The Best of C.L. Moore (Kindle Locations 5345-5346). Diversion Books. Kindle Edition.The seed of "Shambleau" came from the romantic and Victorian eras, by literary movements that gave the world Frankenstein and Dracula. The earliest of these works predate Western fiction by more than a full century. And the connection shows in the story. The Martian mob chasing Shambleau would not have been out of place next to the pitchforks and torches of Universal monster movies. And Shambleau is not an indigene confronted by civilization, but a Gorgon and an outright monster from myth. Strip away the rayguns, and the story could have taken place in the same medieval village that Morris's red witch ran through. It is unfortunate that the jump to label "Shambleau" as a space western shrouds its ties to Romantic literature.