If, into this invented fantasy world, certain assumptions about gender roles, skin colour, sexual preference, etc, are carried ad hoc from our world, then it is incumbent that they be challenged. Why? Because it matters. Because, every time shit like that is carried over, an underlying assumption is made: that such assumptions adhere to some Natural Law, wherein arguments in defense of such choices devolve into falsehood ('history shows it was always that way' [no, it doesn't], and 'in a barbaric world a patriarchy is given' [no, it isn't], or, 'in a post-apocalyptic world where remnants of hi-tech is akin to magic, men will still rule and dominate every social hierarchy' [say what? That doesn't even make sense!]). The Natural Law argument is a fallacy; more to the point, the Fantasy genre is the perfect venue in which to utterly dismantle those assumptions, to offer alternative realities and thereby challenge the so-called givens of the human condition.
You'll recall I've made similar arguments in the past, referencing debates on whether it was "realistic" to have warrior women in fantasy:
Even if you put aside, for the moment, problematic assumptions of biological determinism (and ignoring what social construction processes and social institutions do to constitute and maintain gender “roles”), there’s still one thing I just can’t understand: why on earth would a fantasy world have to conform to the (supposed) rules of this one?
However, as I'm sure you'll agree, Erikson says it best. And there you have it, folks.