Not understanding how conciousness works in our bodies does not directly imply that conciousness cannot emerge in a complex system of fully understood basic components.
Consciousness is directly observable to everybody who is conscious. From there the next logical step is to find out why people are conscious, and right now that's not something that anybody understands. There is presumably something that causes consciousness even though we can only observe the result.
However, saying that a machine is conscious would be to assume your own conclusion. Nobody's observed a machine being conscious. There's no explanation for how a machine would be conscious and there never will be because we already know everything about how they work.
Consciousness is just a bootstrapping mechanism for intelligent behavior and meme distribution. Once an entity is smart enough without it (Likely via an effective set of cultural memes and a good system for propagating them), it will become vestigial much like the genetic selection pressures it displaced as the primary means of adaptation.
I recommend "Blindsight" by Peter Watts for a discussion of that. (It work of fiction but it is a well researched with citations and embraced by the neuroscience community work of fiction)