https://www.youtube.com/watch?v=OsYUWtLQBS0

Zombies aren't real so any reference to them as a legitimate metaphor for a being that acts like a human but has no internal conscious experience is nonsensical. The reason this metaphor is confusing and mostly useless is two-fold.

The first issue is the use of the term "zombie". Zombies are not real and appealing to them as a way to create clarity is a contradiction. It's like trying to understand horses by appealing to unicorns. Unicorns do not have a consistent definition and any definition must contain some amount of supernatural or unreal elements. Because unicorns are not real one can ascribe any characteristic they would like. This makes the concept of "unicorn" open-ended and in no way analogous to anything real, like a real horse. Using something fake to understand something real seems counterproductive.

The concept of "zombie" is similarly vague and inconsistent as the term "unicorn". Some definitions have zombies being able to do different things in different ways. Some zombies can run and some can solve simple problems. Sometimes there are zombie animals. All zombies represent the animal instinct of feeding and violence. All zombies represent something to be feared and one is always justified in destroying them. Zombies tend to represent the evil lurking inside of humanity and in my estimation, they do not offer a useful analogy to anything resembling the average person and offer nothing in relation to understanding consciousness.

The Second thing:

Now, when someone like David Chalmers uses the term "philosophical zombies" they are attempting to offer a juxtaposition between the human that has subjective experiences and the human that does not have subjective experiences. This type of "zombie" is not evil, necessarily, or violent or stupid but is, on its face, indistinguishable to a normal person. If you interact with one of these "zombies" you would say that they were conscious and they would say that they had thoughts and feelings but they would be lying or simply saying things that they think you want to hear. A robot seems like a more obvious metaphor in that we understand that a robot can do things just based on response algorithms as opposed to interacting with its own internal decision-making process, where they debate against themself the options and consequences of actions like people seem to do.

I think that it is actually impossible to imagine and understand something that has all of the same properties and characteristics as a human except this one aspect, subjective experience. It is similar to having a substantive understanding of the concept of nothing or infinity. While we can use these terms to express specific concepts in math or as metaphors for a lack of understanding it is impossible to have a realistic representation in your mind of these terms. When you think about what the term "nothing" means you might think of blackness or the vacuum of space of the number zero or the stillness that comes from meditation or ultimate quietness but none of those things you are thinking about are actually nothing. "Nothing" does not contain any concepts, words, thoughts, analogies, substances or thoughts. Actual nothingness is not a concept that contains anything and we lack the capability of understanding it fully. It is the same with the term infinity and in the concept of the philosophical zombie.

Any contemplation of an entity that acts exactly like a person but somehow isn't a person is a contradiction of how we identify people. We only need the term "subjective experience" because we communicate with others. If a person were never to interact with others then the concept of subjective experience would not have any use and the person would never need to contemplate the concept. The person might have consciousness but the identification of these things would be useless and could never be proven. If the person looked inward and was able to communicate to themself that they were conscious they would have no way to test this theory. Also, the idea that a person would spontaneously come up with language or abstract theories without interaction with others is nonsensical. Some thought experiments are so unrealistic they are actually a waste of time.

On consciousness:

If consciousness is derived from physical processes then there is no reason to hold it as a human-only phenomenon. If consciousness is somehow separate from physical processes then one can say anything they want about it and it would never be provable or disprovable. If something can not be scientifically examined then there is no reason to apply scientific standards. If consciousness is emergent from physical networks or is fundamental within physics then there is no reason to think that robots or zombies couldn't be conscious. Just because we don't have a direct physical explanation of consciousness at the moment doesn't mean that consciousness is something metaphysically special.

So what would it be like to be a zombie or a philosophical zombie? This is similar to contemplating what it is like to be a bat or anything other than a human. Just because we can come up with the sentence doesn't mean it is meaningful. Thinking that it is "like" something to be some other entity puts a lot of value in the human imagination. Human creativity and imagination is an amazing tool but it is not an all-knowing power and is rarely accurate scientifically. It is certainly fun and can help to push past certain obstacles of understanding but it isn't a form of divinity that supersede or replace scientific rigor and logic. Just because we can imagine something doesn't mean anything important. The human mind can combine and exaggerate concepts to no end but none of these imaginings should be used as doctrine. Just because I have a dream about something doesn't mean I should act on that imagining.

I'm not sure it "is like" something to be me. My experience of myself is not reducible to a likeness or analogy. If someone were to ask me "what is it like to be you," I could try to answer in many ways. I could say, "well it is the same as anyone else. I wake up. I eat. I sleep. I have thoughts and feelings. I get anxious and experience happiness at times," but is this what it's "like" to be myself or is it just some language that I think the other person might relate to so that I don't seem like a robot or psycho to them? Any attempt to reduce the human experience to what it is "like" to be them is necessarily lacking in detail. Also, all this is "likeness" talk is dependant on language and language may not be capable of describing an accurate model of experience and so there will always be a lack of understanding as we try to map non-linguistic information (feelings) onto language.

This is not to say that language is not useful or helpful it just isn't the entire story when it comes to human experience and consciousness. Consciousness and language are inexorably linked in our communication of consciousness. Our ability to communicate allows for concepts in general and the concept of consciousness seems to be limited by our ability to use communication tools. Language is just one way to communicate so maybe what it is like to be something is better communicated by some other artform. Maybe what it is like to be someone would be communicated better by creating a multimedia artwork that involves all the senses including emotional senses induced by drugs. Maybe what it's like to a bat is closer to what it's like to be on cocaine all the time. I'm not sure how to test this theory.

Also, I'm not sure if consciousness is the only germane factor in ethical considerations. A person in a coma still retains some ethical considerations even if they may never get out of their coma. Using the desire to understand consciousness as justification for ethics doesn't seem to be a sufficient reason. Justice isn't an entirely logical endeavor and relies on emotional intuitions many times. Our sense of justice is often invoked by feelings.

Top-down versus bottom-up.

I like bottom-up explanations so, to me, looking at consciousness as a top-down phenomenon is difficult to understand. You have to take consciousness as given and I don't know why one would do that. We think that consciousness is a certainty but if the history of science shows us anything it is that skepticism is more useful than certainty. Taking consciousness as a given allows one to move past the problem of what creates it and allows one to think of what the effects of consciousness are. This is useful to solve other problems but taking consciousness for granted is not a way to understand what consciousness is on a fundamental level. It is the same as quantum physics. Taking quantum physics for granted allows people to understand its consequences but it doesn't lead any to understand what underlies its existence.