Ursula Le Guin, though she makes a big fuss out of the "thought-experimental" nature of her novel, and explicitly says that she's not trying to make a political statement such as "we damned well ought to be androgynous" - but even so, she seems to intentionally pad levels of ambiguity â€“ maybe even excuses, plausible deniability â€“ into any possible "message" of her novel.
One of the biggest features of Gethenian society that seems to contain a hidden moral supposition is this: "they [do] not go to war" (48). The clarification: "they behaved like animals, in that respect, or like women" (48) â€“ the mention of women especially hints that Gethenians are incapable of going to war because they are too feminine, and women don't go to war. (Personally, I don't take that for granted, but for the sake of argument, I'll let it go.) The problem is that their peculiar androgyny is not the only defining feature of Gethenian culture â€“ they also live in probably the coldest environment among the novel's known inhabited planets. It is a well-supported theory in life outside this novel that geography and environment are determining features of culture (see: "Guns, Germs, and Steel"); and that makes it believable that the Gethenian inability to mobilize is the result of their weather. Consider: going to war is an enormous undertaking; oftentimes in the past, wars had to be postponed during winter months. Part of what made Hannibal an amazing general is that he managed to cross the Alps, which are snowy all year round, and even then his army suffered massive losses. The Gethenians would have to face that sort of weather everywhere, almost all the time; war would be a massively wasteful, unproductive undertaking for them, in comparison to our wars (and that's assuming that real wars are productive!). It's impossible to rule, therefore, that their androgyny is what makes Gethenians unwarlike; but it's also impossible to rule out that possibility.
Even within the novel, "it seems likely that [the Gethenians are] an experiment" (89). But what kind of experiment are they? If they were meant to be set up in opposition to other humans, then the experiment is critically flawed, because there is no strict control â€“ there are two variables, ambisexuality and extremely cold weather. For a realistic scientific experiment, the constraints are too loose, for the reasons I've already spelled out. However, the idea that Gethenians exist on account of "human genetic manipulation" (89) is a convenient one for avoiding difficult issues such as proposing that such an evolution from humans is possible, likely, or natural. Otherwise, one might suppose that Ursula Le Guin was suggesting that humans would eventually become this way; or that humans could just have easily turned out this way. But instead, she sets down the opposite notion: that this sort of thing is nigh-impossible, and exists by mere contrivance. She calls attention to the falseness of the situation in such a way that it seems to discredit value judgments of any kind. The Gethenians are not explicitly better or worse, by any standards, than normal humans; they are just different.
And this sort of thing is all over the novel. It's almost as if Le Guin knows she's treading on sensitive ground here, and so she restrains herself from making any claims that could be construed as outrageous. Whether in doing so, she undermines the meaningfulness of her novel or allows it to be all the more insidiously thought-provoking is anyone's guess.