In which case, you will be making a point - not that there are different facts, but that there are different languages. Of course, language is an invention - and there is no natural law that dictates the definition of the word "astronomy".
It is merely a convention that we have adopted a language in which the term "astronomy" does not cover chemical facts. But we could have selected a different language - and there is no law of nature dictating that we could not.
And, yet, these facts about language - these facts about the ways we define our terms - does not cause science to fall to its knees either.
So, what are you talking about? Are you talking about morality, or are you talking about "morality"?
I think the fact that astronomy means astronomy and not chemistry among rational conversationalists is as significant as the fact that the chess piece that looks sort of like a horse is the one rational chess players use as the knight.
I don't think there is anything particularly significant in almost all labels, they're positive use is that you can manipulate concepts and report on your results to others using them.
Do you believe in an objective morality capable of being scientifically investigated (a la Sam Harris *or others*), or are you a moral nihilist/relativist? There seems to be some division on this point. I would have thought Less Wrong to be well in the former camp.
Edit: There seems to be some confusion - when I say "an objective morality capable of being scientifically investigated (a la Sam Harris *or others*)" - I do NOT mean something like a "one true, universal, metaphysical morality for all mind-designs" like the Socratic/Platonic Form of Good or any such nonsense. I just mean something in reality that's mind-independent - in the sense that it is hard-wired, e.g. by evolution, and thus independent/prior to any later knowledge or cognitive content - and thus can be investigated scientifically. It is a definite "is" from which we can make true "ought" statements relative to that "is". See drethelin's comment and my analysis of Clippy.