"Turning a person into paperclips is wrong" is an ethical proposition that is Eliezer-true and Human-true and >Paperclipper-false, and Eliezer's "subjunctive objective" view is that we should just call that "true".

Despite the fact that we might have a bias toward the Human-[x] subset of moral claims, it's important to understand that such a theory does not itself favor one over the other.

It would be like a utilitarian taking into account only his family's moral weights in any calculations, so that a moral position might be Family-true but Strangers-false. It's perfectly coherent to restrict the theory to a subset of its domain (and speaking of domains, it's a bit vacuous to talk of paperclip morality, at least to the best of my knowledge of the extent of their feelings...), but that isn't really what the theory as a whole is about.

So if we as a species were considering assimilation, and the moral evaluation of this came up Human-false but Borg-true, the theory (in principle) is perfectly well equipped to decide which would ultimately be the greater good for all parties involved. It's not simply false just because it's Human-false. (I say this, but I'm unfamiliar with Eliezer's position. If he's biased toward Human-[x] statements, I'd have to disagree.)

I disagree with that approach because this is exactly what is called being "subjective" by most people

Those same people are badly confused, because they usually believe that if ethical propositions are "subjective", it means that the choice between them is arbitrary. This is an incoherent belief. Ethical propositions don't become objective once you specify the agent's values; they were always objective, because we can't even think about an ethical proposition without reference to some set of values. Ethical propositions and values are logically glued together, like theorems and axioms.

You could say that the concept of something being subjective is itself a confusion, and that all propositions are objective.

That said, I share your disdain for philosophical word games. Personally, I think we should do away with words like 'moral' and 'good', and instead only talk about desires and their consequences.