In other words if we can observe a machine thinking about its own (symbolic) thinking, then I think it's conscious.
Consciousness is the ability to observe one's own mental processes and make sense of them symbolically. That is one possible definition of it.
You are right that we can't really prove that humans are conscious, because we cannot observe their thinking.
But, to prove that a machine is conscious all we need is to agree on a definition of what it means to be conscious, because machines can be easily inspected. And then find a machine that demonstrates features that fit the definition.
If we can't agree on what it means for something to be conscious then the whole question of whether some AI is or could be conscious is of course meaningless.
I have the feeling that attempts to create conscientious AI will just result in paperclip maximizers that have to use rationalization as an indirection layer to engage in their paperclip maximizing behavior.
Not much of an improvement, but realistically, what other result would be tolerated by whoever is building a DWIM AI to run a paperclip factory and for whom conscientiousness would just be a regulatory box to tick?
No, you think that's possible but it's naive. Your existence depends on environment and self replication of information. Your structure depends on it, your cognition. Are you saying you can be separate from the tree, and everything just a fake around you?