It's not that there are "data" to support the idea, but there is the fact that consciousness is unobservable. That is weird and different from all other physical phenomena, wouldn't you say?
It's complex, it's hard to define, but it's definitely not unobservable. Also, as a mere physical manifestation, you can fiddle with it in a pretty physical fashion. You can put in on drugs and watch it warping. You can toy with its physical structure surgically and see how it gets messed up (wonderfully discussed in Oliver Sacks' books), you can bump it with a boxing glove and literally switch it off.
Too much interactive for an unobservable phenomenon.
What makes it weird and different from physical phenomena is the fact that it is not generally observable, even though it is posited to exist for all people.
Or do you disagree even with that? If you do: I don't just mean that it doesn't emit visible light. I mean it doesn't emit anything. Consciousness is just the fact that the universe exists from a perspective. It is not an object, "out there", "in the world", but something only experienced by each consciousness for itself. The mere fact that we could create a perfectly convincing AI and then still have doubts about whether there really is "anything in there" is a result of the fact that consciousness is unobservable. Does that explain well enough what I mean?
In fact, because of the fact that it is unobservable, you cannot even make a reasonable argument that the netbook I'm typing this on lacks consciousness.
I for example can argue that anything that is executing a series of algorithms as part of a system has consciousness, and therefore this computer is quite conscious, just as I am (even though my series of algorithms is much less well-defined and reproducible.)
Your own feelings about your consciousness are unimportant to define consciousness. It's definitely irrelevant that you can't "experience" how other people feel the colour yellow, we still regard it as observable. The only difference is that we can define "yellow" as electromagnetic radiation with certain wavelengths, whereas we'll have to wait a bit to get an equally satisfactory definition for consciousness.
We shouldn't attribute a special epistemological status to the brain/mind/consciousness just because it's complex and we don't know it very well and just because it's ours.