Ethically loaded? How? I don't see how the brain would be suffering? Or are they worried about skynet?
Here in meatspace, putting a human in a sensory deprivation tank is torture and one of the more surefire ways to drive a person insane. The brain isn't wired to believe in null sensory data. If a region of the brain stops receiving stimulation, it frantically strengthens its connections to other regions, tapping randomly into its neighbors and interpreting their arbitrary stimulation as sense data (compare the hallucinations of sensory deprivation to phantom limb syndrome and somatosensory remapping in amputees, e.g. touching an amputee's face triggering sensation on the amputee's phantom fingers because the face and fingers are next to each other in the sensory map of the postcentral gyrus). If this frantic effort fails and the brain regions can't find a source of stimulus, they start to die outright, nerve by nerve, because nerves are wired to commit suicide if they don't fire regularly.
But even a sensory deprivation tank still provides senses of sound, proprioception, temperature, gravity. If we were to create an accurate nerve-by-nerve simulation of an entire vertebrate brain and then provide it with no sensory input.... Well, at best the result would be phantom body syndrome. At worst, it could go well beyond torture and become the greatest suffering ever inflicted on a single sentient being. And we don't understand the brain well enough to know which pieces of sensory data must be provided to maintain sanity and prevent existence from being torture.
And that's not even getting into the legal and moral issues. Let's say we can put a sane mind on a chip by cloning the synaptic structure of a recently deceased human and feeding it all the appropriate sensory inputs. Is it a person? Is it a citizen? Can it consent to a contract? Is it a minor until the hardware turns 18? May I enslave it? Is it ethical to feed it false sensory data culled from a virtual reality simulation, i.e. trap it in The Matrix? If I turn it off and erase it at the end of my scientific study, have I murdered it? If yes, am I legally obligated to keep it powered until the hardware fails? Am I morally obligated to transfer the synapse data to new hardware before the old hardware fails, making the uploaded human immortal? Alternatively, am I morally prohibited from doing that for more than N years, for some value of N? If I'm transferring the mind to new hardware, and my mistake causes a power surge that erases its synapses, am I protected by existing Good Samaritan laws, or have I committed involuntary manslaughter? As it's a simulated human mind, complete with all human appetites, am I obligated to provide it with pornography and the means to masturbate itself to orgasm? Do I have to obtain consent from the human whose deceased mind will be used to create the chip? Am I obligated to pick an atheist, or more to the point a subject who doesn't believe in souls? How well informed does the consenting subject have to be before dying? Does the family have to consent as well, or are we content with provoking another HeLa controversy for the greater good? And so on...