[fasterik]

I don't think "article of faith" is the right phrase. For every possible hypothesis, we attach a prior probability and then we update those probabilities when new evidence comes in. If accepting a given hypothesis would require changing a lot of other hypotheses that we have high confidence in, then we should attach a low prior probability to it. I don't have to take it on faith that a low probability hypothesis is false; the default position is to assume that it is false until compelling evidence to the contrary appears.

For example, I can hypothesize that a fifth fundamental force is needed to explain consciousness, but then I need to modify the standard model of particle physics to account for new interactions. I have a high confidence that the standard model is correct in the domains relevant to the evolution of life on Earth, namely chemistry and biology. So my default assumption is that we don't need to introduce new laws of physics to explain consciousness.

>Is a (functional) brain both necessary and sufficient for consciousness to "emerge"?

I think you misread my post as implying that a brain is required for consciousness. Our baseline for talking about consciousness is consciousness in humans, and all of the medical evidence suggests that human consciousness is associated with brain activity. But I see no reason to believe that something made out of silicon or other non-organic materials couldn't be conscious if it implemented the same kind of processes that we find in the brain.