edit: accidentally removed the quote i was commenting on when editing in Stross' comment, here it is again:
a belief in psi powers implicitly supports an ideology of racial supremacy, and indeed, that's about the only explanation I can see for Campbell's publication of the weirder stories of A. E. Van Vogt.
Maybe it's me but I don't think that is so self evident a claim to be posited without further explanation.
Best I can come up is he means the necessary implication of having superabled people in a fictional setting is that you have a de facto racial elite, even if the concept rarely breaches the surface of the text, like in the unfortunate sequel to the Dark Knight Returns by Frank Miller.
Edit: he addresses it in the comments (can't find a way to direct link from phone, its comment #14) I wasn't far off:
If you're a glutton for punishment, (re-)read Slan by A. E. Van Vogt.
Secret superrace with super-mind powers! It's totally a meme in vintage SF (goes back at least as far as Bulwer-Lytton's The Coming Race in the 19th century) and you rapidly end up with eugenics and breeding for desired traits (eg. psi powers).
I got introduced to the genre through Star Trek and I always found its moral vision, in addition to all the weekly alien weirdness & how it was approached with patient curiosity, strongly appealing. Roddenberry set out to create an explicit alternative to the impoverished perspectives of the Cold War era. The Prime Directive is non-interventionist to a fault.
Gotta have to push back on that. Certain genres are, but even the ones that are written nowadays and explicitely in the space opera genre tend to try to grapple with the ethics of colonialism.
Greg Bear's Hull Zero Three is set aboard a colony starship that's revealed to be chock-full of genocidal weapons to ensure that the target planet isn't a problem for humans to settle on. "Are we the monsters" etc.