I think the existence of zombies would contradict certain laws of nature in our world. It seems to be a law of nature, in our world, that when you get a brain of a certain character you get consciousness going along with it.
Because the idea of zombies seems to make sense, and seems to, in a certain sense, be possible, I think one can use that to argue against the thesis that everything is purely physical. Now many people, I think, agree that the idea of zombies are conceivable, including people who want to be physicalists.
I think that consciousness has always been the most important topic in the philosophy of mind, and one of the most important topics in cognitive science as a whole, but it had been surprisingly neglected in recent years.
There's certainly nothing original about the observation that conscious experience poses a hard problem.
Sense data are much more controversial than qualia, because they are associated with a controversial theory of perception - that one perceives the world by perceiving one's sense-data, or something like that.
I had the idea that it would be wonderful to be a physicist or a mathematician maybe 500 years ago around the time of Newton when there were really fundamental things just lying around to be discovered.
