In a recent interview published in vol.26 of the academic journal Paradoxa (and unfortunately not available online), Junot Diaz cogently free associates on the relationship between the science fiction imaginary and the material facts of 19th and 20th century imperialism. Here's the provocative quote that made me wonder why I'd never thought of this:
I’m not alone in noting the irony that a genre like sf, historically obsessed with alterity, should have so much trouble with actual people of color and women and LGBT peoples. But when one understands the degree to which nearly all our genres are haunted by, and have drawn a lot of their meanings, materials, and structures from the traumatic Big Bang of colonialism and its attendant matrixes of power (coloniality)— irony strikes one as the least of our problems.
Alien invasions, natives, slavery, colonies, genocide, racial system, savages, technological superiority, forerunner races and the ruins they leave behind, travel between worlds, breeding programs, superpowered whites, mechanized regimes that work humans to death, human/alien hybrids, lost worlds—all have their roots in the traumas of colonialism.