Psychic abilities appear in much of the explicitly identified Traveller source material -- it was as much a part of the
Known Galaxy as
neofeudalism.
In Traveller,
anyone could potentially be a psionic with some luck and the right training. Adventure 0 suggests (p. 7) that seeking out a psionic institute is a common early goal for player character groups. The "public prejudice" rules have some echoes of witchcraft trials, but the stigma is about what psionics
do rather than what they
are or how they look. It's analogous to intolerance for sexual deviance (perceived as a choice), say, versus racism.
I'm resisting Van Vogt as the source because the Slan were overtly superhuman and physically identifiable as a separate subspecies. The Henderson and Key alien psychics were also genetically distinct, but at least physically indistiguishable.