>"nihilism" This is a minor stylistic point, but I think it is better to avoid using this word in online writing, since it lends itself too easily to misunderstanding. You are using it here to describe views like "there is no positive-valued well-being," but it is also widely used to describe views like "there is no such thing as moral value at all," or even "there is no such thing as *objective* moral value (but subjective moral value can still be important)." These views are very different fr…
The tedium of explication is precisely why the short, familiar label is often worth using -- so long as the intended meaning is clear enough from context (or doesn't make a huge difference). In this case, my reference bracketing "outright nihilism" is to the view that there is no such thing as moral value at all. Just flagging that I'm not arguing here against radical skeptics or error theorists who think we've no basis for attributing value to anything. But for the rest of us, if we allow for …
I think "quasi-nihilistic" is less objectionable, since it will at least give readers pause and force them to consider whether or not they really understand what you are talking about. As for the metaethical case, I don't think there is anything objectionable about presenting an argument that "moral antirealism amounts to a form of nihilism" (I think the argument would fail, but that's another matter). However, I would find it objectionable if someone were to assume that their belief they possess such an argument (whose success or failure remains contested) justifies them in referring to moral antirealists as "nihilists" in contexts other than the presentation of that argument. Apart from anything else, it would just muddy the waters of discourse and make it difficult to know what anybody is talking about, especially in an online context where we are always already subject to the temptation to play a little fast and loose with our terminology. A silly analogy: Suppose I think I have an argument that non-naturalist realism entails theism, but most non-naturalists think my argument doesn't work. It would be bad discursive practice for me to subsequently refer to moral non-naturalism as "theism," because it would be a misrepresentation of their views. (I think this would still be true even if people who were not non-naturalists generally accepted my argument.)