Earlier quoted context omitted.
Consciousness is the basis of human rights not because of it being a featureless "flag". It is because it leads you to you assume, all other humans would experience the world in essentially the same way you do. When you revert to withholding human rights from entities that don't meaningfully differ from yourself, you negate the case for your own human rights itself.
Is it, though? If we ever found other species that were consciousness they wouldn't automatically be "human" nor would they have the same legal rights. That's as simple as looking at the many countries that treat different castes, women or minorities differently. In parts of America a zygote has human rights.
This is the tricky part, you can never know. Scientifically speaking, and logically, you can never ever tell something is conscious. We all assume we all are, because we're very similar to eachother, thus you must have what I have, my subjective experience of reality. That's it. That's what we all base our human consciousness on. Agreeing we must have it, since we are very similar in shape/structure/behavior. That's all there is to it.
We are not scientific consciousness detectors, we just got used to assuming we all are. That is why we never really extended it to animals, because we cannot scientifically know, only agree on it, and that's not very lucrative for the people who can decide if humans officially agree animals are conscious or not, because of farming, because we need to displace or even wipe whole species to use the resources from their lands.
There's also religious reasons to deny animals consciousness, which again is practical aspect shoved into religion, to help with less debates around this subject, makes things easier.
So in the end it will always be a collective decision. Or a political one at least. If and when we decide something other than us is or isn't conscious.
Also remember, just because it acts conscious doesn't mean it really is. A piece of software that is not even based on LLMs can act conscious. So could a biological alien, it could act conscious but we can never know, we can only decide.