
It's nothing whatsoever to do with regarding consciousness as supernatural magic.
Then why does it matter whether it happens inside my head or somewhere else? Scientifically, what is the difference? Why does it matter whether it's inside my head or inside a thermometer?
Nobody here thinks that people do not have opinions on moral matters. Nobody here thinks that these opinions are not just physical things going on in their brains - or if they do they are superstitious idiots and I discard their opinion. Everyone here is on exactly the same page as far as that goes.
The problem still remains that you can't get from any number of "is" statements about people's brains to a moral "ought" statement.
Right, not without understanding what "ought" really means, which we don't.
Okay, so people hold some moral opinions. What now? How do you get from there to a conclusion about morality?
By understanding what "ought" really means. Right now, we only understand morality as things that "seem right to us", just as we once understood colors only as things that "seemed red to us". So we can't get from "the sky looks blue" to "the sky really has these properties that make it look blue to me" because we don't know what those properties are. But once we understand how humans actually make such judgments, we should be able to trace the input to the output. Then we should be able to separate the objective property from the subjective judgment of it.
What happens if we meet aliens whose brains are wired up so that they reach entirely different moral conclusions about the same states of affairs? Are we both right (moral relativism), or are you actually going to try and tell us that there is a True Universal Morality and as a matter of fact the aliens are wrong? Or that because there is True Universal Morality no such aliens could possibly exist as an article of faith?
We are both right, but this is not moral relativism.
Suppose two people look at an object. One says "this object is tall". The other says "this object is short". Is this height relativism? Does this prove that object's sizes are subjective? The height is an objective property, however judging it to be 'tall' or 'short' is contaminated by subjective biases -- as all measurements made by humans are. Science is very good at filtering these out given enough time to understand how the perception or judgment at hand works.
If the aliens had a more limited range of color vision than us, they may say two things "seem the same color" to them and a normal human will say the two things "seem different colors" to him. They are both right because the two things are objectively such that they seem different colors to people with normal vision and the same color to our aliens. We can very precisely say what objective properties make this happen because we understand very well how people make such judgments.
Again, all properties are relational in this sense. Saying that a ball is blue means that when white light hits it, the reflected light has a mix of frequencies that appears blue to normal human vision. How is what happens when light shines on a ball any more or less inherent in the ball than what happens when a human evaluates the morality of an action inherent in the action? It is an objective fact that what measurement you get depends on what and how you measure. It is the norm for two measurements of the same objective property made by different 'meters' to differ.
That something "seems right to me" is such a contaminated subjective judgment. We don't yet know enough to figure out what the corresponding objective properties are. The problem is, we don't yet know what "really ought" means just as we once didn't know what "really blue" meant -- which objective properties cause us to judge something to be blue.