In my opinion the only value in this idea is that it highlights the absurdity of trying to apply an empirical model on an un-empirical concept. Since "consciousness" can not be measured, and indeed is difficult to even define in words, it is excluded by any model which insists upon an objective reality.
To your point: how do we know that all people posses consciousness? We don't. We make that assumption because other people are like us. The less like us something is, the less likely we are to assume it has consciousness. For most of human history animals were not afforded this assumption and that is only now starting to change because, as it turns out, animals are a lot more like us than we like to admit.
In other words, it's speciesism. The whole discussion about what does and doesn't have conscious is a desperate attempt to justify human exceptionalism.
>We make that assumption because other people are like us.
Yes, and I think this is a mistake, because it shuts down any hope of isolating what it is about us that makes us conscious. Perhaps this will change as human-lookalike-robot technology gets better, breaking down the "looks like me, must be conscious like me" argument.
People are starting to grant animals the rights of consciousness, but let me ask, what about sperm? I myself was sperm once, and over time I became a full-grown human being. If consciousness is a boolean, then at what exact moment did I become conscious? Was it when I reached the egg? When the first neuron in my brain formed? When my umbilical cord was severed? When I first recognized myself in a mirror [Lacan]?
> If consciousness is a boolean, then at what exact moment did I become conscious?
There's a simpler answer: there was never a state in which you were not conscious. And yes, that would apply to literally everything in the universe, and in every grouping of such things imaginable, and in fact 'you' are neither a single entity, nor a gestalt of several, nor merely a component of another, 'you' are all these things at once.
But the real point I'm trying to make here is that these questions are literally meaningless if you insist upon empiricism because they are untestable.
We don't and can't. Because we can't even come up with a universally accepted definition, there can be no bright-line test.
Coupled with our innate arrogance, where we allow ourselves to "just know that we are", just like we are pretty sure that we get to exert "free will", you end up with a lot of sloppy thinking. I'm not claiming to have any answers (I'm more of an intentionally extreme skeptic of the answers I come across), but I don't think you can deny that there is a lot of sloppy thinking (esp. on a layman's board like this) around "consciousness", "intelligence" and "free will".
To your point: how do we know that all people posses consciousness? We don't. We make that assumption because other people are like us. The less like us something is, the less likely we are to assume it has consciousness. For most of human history animals were not afforded this assumption and that is only now starting to change because, as it turns out, animals are a lot more like us than we like to admit.
In other words, it's speciesism. The whole discussion about what does and doesn't have conscious is a desperate attempt to justify human exceptionalism.