You missed "The Right Hand of Darkness".
And I admit I haven't watched too much Star Trek. But I think the point still stands that this works are clearly of different genres, and still it would seem wrong to say any of them isn't science fiction.
If you're referring to Le Guin's "The Left Hand of Darkness," I would propose that the Hainish universe's Ekumen and Star Trek's Federation share a similar flavor. Moreover, both bodies of work engage in speculative anthropology, although Le Guin's treatment has, in my opinion, considerably greater philosophical depth. This is not necessarily to dispute your contention, but just to point out that they share thematic elements beyond just the science fiction umbrella.
