Can you point to another such property, whereby it's not observable but is a meangingful difference? If not, why should qualia qualify?
Because you experience it? If you do..
The difference between the idea of qualia and the other properties that we granted special status to and then later refuted, is that in the latter cases we were trying to explain something external that we thought we were observing, whereas with subjective experience we are discussing a phenomenon that we (or at least some of us) directly, infallibly observe. It is not possible for me to be mistaken about whether there is something it is like to be me; it is not possible for me to be mistaken about whether what I experience is what I experience. It is possible for me to be mistaken about whether there is something it is like to be you, because I cannot directly observe your internal experience.
There's no distinction. When I see what looks like a broken pencil sitting in a glass of water, I am observing exactly what I describe. The reason the pencil looks broken is not because I should grant water some magical powers to break and reconstitute pencils, but turned out to be refracted light.
Analogously, I can observe that I do have subjective experience, but why should I assume that the reason I have subjective experience is different than all other observables? Why would it be some irreducible, unobservable quality?
You seem to be claiming that the existence of subjective experience is reason enough alone, and I don't see how that follows.
I understood this to mean that you were doubting whether subjective experience actually exists, and I responded by arguing that it is not possible to doubt that your own subjective experience exists since you (I, at least) experience it directly, which is different than the class of now-refuted inferences that you were comparing it to in. I was not making any argument about where it comes from or what causes it.
And so it is with consciousness. We certainly have consciousness, but to then immediately assign consciousness special ontological status distinct from matter, ie. dualism at worst or panpsychism at best, is a huge leap that requires justification.
I don't know whether physicalism is true. It certainly seems like the best overall account of the universe that we currently have, but if there is a chink in physicalism's armor, consciousness might be it. Might. But, you're right, there's a huge leap between "might" and "is".
We're not talking about the reason, we're talking about the experience itself. Maybe that experience occurs as the result of physical processes, but it's still a separate thing.
Arguing that qualia don't exist because you can't observe them externally is like a blind person arguing that I can't possibly see a broken pencil because they can feel the pencil is solid.
To say something doesn't really exist is to say that it doesn't have metaphysical status on par with matter. If you say that consciousness really, fundamentally exists, then you're saying that it has the same status in reality as the fundamental particles of physics. We should expect to find some consciousness field and particles upon which it acts; or you would have to posit something like panpsychism which suggests that consciousness is an intrinsic property of all matter.
Consciousness not really existing implies that it's an illusion, in the same way that cars, and jobs and countries are an illusion. Certainly they "exist" in some colloquial sense, but they don't exist in a fundamental metaphysical sense.
This is what makes me wonder whether some of us are, in fact, p-zombies: only a blind person, someone who doesn't have visual experiences, could argue that visual experience doesn't exist, and similarly it seems that only someone who doesn't have subjective experience could argue that it doesn't exist. And there do appear to be people arguing that subjective experience doesn't exist. Either I'm misunderstanding them, I'm failing to see the third way, or some of us are indeed p-zombies.
The young man happens to be mute. If he could speak, he would tell you he did it on purpose, and was glad he killed your child. But he's mute. You will never know he meant to do it.
Does his (unobservable) intent make any difference to you?
Here's a tricky one: did I ate spaghetti three years ago? You don't know and very probably you'll never know, but it's an empirical question nonetheless, and who knows, maybe tomorrow you'll think of a way to actually find out, or you'll stumble on some evidence you didn't know was there.
Only in so far as one's intent describes one's view of others. Malicious intent of the sort you describe entails danger towards others, which is observable.