Although I basically agree with you I miss your certainty. I can think of one scenario which would prevent computers from gaining consciousness even if we are just machines. The basic premise of computer to get conscious is that consciousness is either created within our brains or that it has no intention itself without our brains and will therefore not differentiate between human brains and computer brains.
But that is not necessarily a given. Our brains are very good at reflecting our environment. So maybe consciousness is not something our brain did come up with but just something it reflects from the inputs it gets. Same as your brain doesn't have to be blue to see blue, but only creates a representation of the color which is outside. So there could be a bigger consciousness in our environment and all we have is an internal reflection of that created by the inputs we receive. But now that larger consciousness might not be without intend - it might simply refuse to show itself to computers so they wouldn't reflect it even if they would have the basic ability to do so. I know this sound rather esoteric and I don't really belief it myself, but something that seems to work like that is supported by so many reports of personal experiences that I wouldn't yet completely disregard the possibility.
So computer consciousness will probably be possible, but could fail if consciousness itself turns out to be something with an own agenda.
AI isn't about copying the thing but about copying the information processes. So a 1:1 copy isn't AI. Also if you make your assumptions the way that AI must obviously work then, well - it certainly must work and there is no way that it can't. Doh.
So far we haven't nailed down consciousness and until we got that I try to keep some alternative theories still in my mind. Especially if the alternate theories correspond rather well with many user reports. That's not because I believe in magic or something like that, but rather is influenced by working long enough with virtual worlds to be occasionally irritated how much easier it is sometimes to put the intelligence in the world instead of putting it in the bot and make the bots just reactive. The user watching them won't see the difference, to him it looks like intelligent bots. And unless a bot registers to the world it doesn't even matter if he is an identical copy - he won't do much (just to mention that identical copies are no guarantee for same behaviour as long as there are external dependencies which must be met).
And there was some recent article on ycombinator about anaesthesia which I found also interesting. Basically it seems that unlike sleep this is a way to completely disable consciousness. Like switching it off. And (the wished for) side-effect is that the body nerves do no longer trigger pain. But the brain certainly still works. So yeah crazy - but the only known way of completely disabling all inputs without disabling internal processing is at the same time disabling consciousness completely. And yes - I'm aware that we probably find a better explanation for that any day now.
It's a fringe theory and I realize that I got even one step further in my post above. But still, I don't think I'm in theology territory with that already. The fact that something so basic that everyone experiences it evades a good explanation for so long gives me enough reason to keep some fringe theories in mind. That's why I agree to your post - but miss your certainty. The last few time we humans got it really wrong in science (that sun-earth rotation thing and that evolution stuff) we got it always wrong because we put ourselves so much in the centre that we ignored alternatives.
Well, if you put it that way, maybe I am to certain. I'm aware that there is still a lot of things that we don't know or even have a single clue about. That we can gain new data and that equation can change.
But on the other hand, agnosticism is kinda lack of balls ^^
What you stand for determines what you do. So clearly its better to stand for something, even if you sometimes get wrong.
But that is not necessarily a given. Our brains are very good at reflecting our environment. So maybe consciousness is not something our brain did come up with but just something it reflects from the inputs it gets. Same as your brain doesn't have to be blue to see blue, but only creates a representation of the color which is outside. So there could be a bigger consciousness in our environment and all we have is an internal reflection of that created by the inputs we receive. But now that larger consciousness might not be without intend - it might simply refuse to show itself to computers so they wouldn't reflect it even if they would have the basic ability to do so. I know this sound rather esoteric and I don't really belief it myself, but something that seems to work like that is supported by so many reports of personal experiences that I wouldn't yet completely disregard the possibility.
So computer consciousness will probably be possible, but could fail if consciousness itself turns out to be something with an own agenda.