If you simulate a physical brain, but give it no input, what is the output? Consciousness? Look, fundamentally we've had "human brain hardware" for years now. A Turing machine is a Turing machine is a Turing machine. If you know the mathematical formula for emergent consciousness, there are a bunch of people who would be excited to talk to you.

Why assume it gets no input? (Why build it if not to interact with it?)

A grown, working brain has been shaped by its input – changing the connections, the chemical balances, and other things we don't yet understand (but someday will). So when talking about a 'simulated brain', I think an embedded history of meaningful input, and continued interaction, is implied.

(Also, creating such a brain and then depriving it input might be torture, as with extended sensory deprivation in natural humans.)

You seem to be unduly assuming emergent behavior. First, we do not know how to completely mirror a human neural network. Second, even if we did we don't know how the initial input affects emergent intelligence.

I'm not saying it's impossible, but I am saying that you're taking a rather unscientific leap of faith.

I'm not assuming anything about what's possible.

I take issue with your assumption that there is some 'clear' distinction between the goal of '"building a simulation of the physical brain hardware" and the 'goal to simulate human consciousness". A distinction, if any, between those goals is anything but clear.

Further, the people most interested in 'physical simulation' also tend to be 'materialists' who think a suitably precise simulation can reproduce everything interesting about a human mind, including 'consciousness'. Without any personal 'leap of faith' as to whether that's true or false, this is an interesting and deeply murky question.