You're framing this question in an unhelpful way.

Better: what are the major arguments for the position that machine consciousness is not possible? What do I think of those arguments? Particularly taking care to distinguish:

- does the argument prove what the people advancing it think it proves?

- do I find myself agreeing with the argument?

Major lines of argument I've heard:

- the metaphysical argument: consciousness derives from having a soul somehow linked to your brain (and thenceforth to your body); the purported impossibility of "machine consciousness" follows from a belief that only people have souls (of the right type, at least)

- the limited-smarts argument: consciously building a conscious machine is beyond the capabilities of a conscious entity (of our type of consciousness)

- the "difference between silicon and wetware" argument: this ranges from assumptions there's quantum magic in parts of the brain to assumptions that the brain organization implements some other, unsimulable-by-silicon computing architecture (perhaps super-turing)

- the "consciousness is an illusion" argument: consciousness and intelligence per-se have little to do with each other despite the apparent overlap one perceives from reflection on one's own thoughts. Thus machine intelligence seems to be possible but that says nothing about consciousness per se.

If you're really serious enough about this to consider making it a life's work (or because you really want to make a conscious AI) I would suggest taking none of the above arguments lightly, even though it's somewhat fashionable in some circles to assume most of the above are just nebulous handwaving by anti-rational mystics.

"Taking them seriously" doesn't mean "pack your bag and go home"; it means you keep thinking scientifically and analytically and try to answer questions like:

- suppose smarts are limited, but we don't know that yet for certain. What could this intuition mean (in a more formal or more precise sense)? How could I make the intuition more precise? What would a formal proof of the intuition look like (and what would be the theorem)? Does this inquiry seem to be leading me in the direction of possible theorems or nontrivial facts about the expressive power of symbolic systems (that aren't already known, or a retread of Godel)? Does there still seem to be work I'd be interested in doing in this general field if it turns out that smarts are limited?

...as even "wrong" counterarguments can do wonders for pointing you in the direction of interesting questions

Extra Credit: of the researchers who at least seemed to think they'd solve the problem pretty quickly, is there a recurring pattern to be found in the failures those researchers encountered?

Major recurring themes: people who've thought they were within reach of making conscious machines typically assumed that the part of their own nature that they valued most was the keystone to consciousness and assumed everything else was either secondary or easy (and thus could be filled-in later).

Thus a Hofstadter-type -- who loves delving deep into various piles of work and crafting new and insightful analogies -- winds up thinking that the core capability an artificial intelligence needs is the ability to craft such analogies; people with phds in mathematical fields and a more logical bent assume that the core ability is symbolic inference, and make software that does symbolic inference; yet others assume that rational hedonism is the core and work on utility-maximizing decision-theoretic planners and agents; others still love making systems with complicated interactions and seeing what pops out and start chasing emergence.

All of that work is good work and has found applications, but the dynamic is obvious: people who get into the field with the specific goal of making AI -- instead of, say, improving algorithms for multicamera view synthesis with applications to industrial quality control -- tend to radically overvalue whatever intellectual style they happen to be good at, but so far none of those intellectual styles appears to have really scratched the surface of consciousness in the sense you're interested in. Beware your best ideas and favorite subjects!