Yea, in my mind it's more of a case of, if we get to the point where we can simulate one brain properly in this fashion, it's essentially useless.

We can simulate the brain of a Lithuanian man who has been addicted to 2CB his entire life. Great. Now that we have done that, we have essentially just recreated a brain that already exists.

What does this fake brain tell us that we don't already know, after studying this man for his entire life to determine all the inputs required to simulate his brain?

We now have one brain. This is useless in an inferential sense for any kind of research - we have a sample of N = 1, meaning we have a case study of a brain that we already have fully mapped without having to expend the resources to simulate it.

Once we have the capabilities to simulate a human brain properly, we wont need to do it (or learn anything substantive from it). This is the argument I most agree with anyway.

I wouldn't be so quick to distinguish between a biological brain and a computerised one, they exist on such different planes that (in my opinion) such broad statements are bold to say the least. I do appreciate your point though.

It's actually pretty hotly debated whether this would be possible, if you're interested check out the debates around things like the blue brain project etc.

Your brain has billions or trillions of synapses. The information being relayed at synapses is not binary (different neurotransmitters have excitatory/inhibitory effects which can even propagate backwards). The effect of the entire nervous system would need to be modelled, as well as the gut microbiome (these all influence it significantly).

Add onto that, say you manage to create a perfect simulation, you essentially just have a brain in a jar. So you now need to simulate an external environment, a lifetimes worth of experiences to allow the simulated brain to plastically develop in response to input (otherwise it's an inert lump of meat essentially). Your simulated brain will not respond accurately without this plastic development.

To simulate a consciousness accurately, you would essentially need to simulate someone's entire life.

I agree that consciousness is emergent, but I don't think we could simulate consciousness as we know it. I believe we could get to some form of consciousness though.