So, yeah. Doc Smith is obviously a man of his time, by I do give him props for trying to break the mold, even if it looks a bit.. quaint.. to us moderns.Not all such races, it may be said here, belonged to Boskonia. Many essentially similar ones, such as the natives of Palain VII, adhered to our culture from the very first. Indeed, it has been argued that sexual equality is the most important criterion of that which we know as Civilisation. But, since this is not a biological treatise, this point is merely mentioned, not discussed.
That's said, there's some interest to be had in extrapolating from this point. If we assume that most cultures go through an "uncontacted" period before emerging onto the galactic scene, whether they're predisposed to discriminating against their own species could very much set the stage for how they're inclined to react to other species. The narrator might also be referring to more extreme forms of sexual dimorphism; non-civilisational aliens might have evolved with an intrinsic concept of something like ownership/slavery as the natural order of things for example, which could strongly influence their attitude to outsiders.
Now it's been made clear the Civilisation is accepting of other ethical codes in its members, but it's interesting that it's this one that they see as universal - something that could be boiled down to "thou shalt treat thy fellow sapients with respect as individuals", and people who don't hold to this standard, as evidenced by how they treat themselves, do not play well with others.