I believe nature is all there is. If we could replicate a human brain several times, and make each 'human brain' receive the exact same input data (sounds, sights, smells e.t.c.) from the moment they 'exist' until the end of their lifetime, I truly think that each of these brains will make precisely the same decisions (and each of these 'brains' would think they were conscious and in control of their lives).
In my eyes, consciousness is simply a natural phenomenon that can be explained but we just lack the understanding at this moment. Time and time again we have made this mistake of assuming there is something supernatural about the things we cannot comprehend and only a few centuries later it is completely understood scientifically. I think consciousness will be a similar case but will take more time.
You’re saying it’s all 100% deterministic. But at the quantum level, things are probabilistic. The hundred brains with the same input data might make different decisions like how each ball dropped in the Galton board chooses a different route.
But I agree with your overall premise. It can be all understood scientifically. There is nothing supernatural about things we cannot comprehend.
Nature vs. nurture is also a popular debate. This scenario you described, even with nature being all there is, doesn't imply all our actions and thoughts are shaped by our environment.
I think supernatural things don't exist by definition. If ghosts would exist, they would be just natural.
The real question is whether there is a two way link between consciousness and the physical world. Obviously the physical world is observed by consciousness, so that direction checks out. What about the other direction? Is the physical world at all influenced by consciousness? The mindfulness folks seem to argue: no. They argue that consciousness is like a person watching a movie, where the movie is experience. The person is so immersed that it thinks, it controls the movie, but in reality it's a fully passive observer. But this can't be true! Otherwise, the discussion of consciousness could never have come up in human history. A population of "philosophical zombies" could never initiate this discussion. So somehow consciousness must cause physical neurons to activate. The movie knows about the person watching!