Consciousness can arise from an agglomeration of molecules. How sure are you that empty vats (which are made of molecules) are not aware and suffering?

What's going on here? Answer: Fallacy of affirmation of the consequent.

> you must acknowledge consciousness can arise in an agglomeration of human brain cells

That doesn't follow. You could, for example, be a substance dualist. Alternatively you could suspect that there exists some special as yet undocumented property of the human CNS that is required as a prerequisite. Or etc.