P0) 'Human' is a word defined by humans.
Therefore:
P1) Every entity that declares itself human and possesses the ability to define the word 'human' without explicit instruction must be human
P0 implies human is a word created by Homo Sapiens.
P1 implies klingons are human.
I do not trust P1 as klingons are a non human intelligent lifeform.
P0 is an incorrect interpretation.
I mean exactly what I have written: 'human' is a word defined by humans, not Homo Sapiens. Humans are not defined by biology alone, Homo Sapiens, on the other hand, are.
Suppose someone gives birth to an offspring with wings and reproductive incompatibility with other Homo Sapiens (but still sentient in the same way as most contemporary Homo Sapiens). The offspring is, by all definition, not a Homo Sapien, but should, I think, still be accepted as a human being. Unless, of course, that it refuses to declare itself human.
Suppose another species has evolved at the same pace as Homo Sapiens, with near-identical morphology, but remained reproductively incompatible. The two species share an integrated society. It would be absurd, I think, to suggest that the other species is to be considered non-human for legal, ethical, sociological, psychological, and other not-strictly-genetic purposes.
If P1 cannot be accepted, I see a dark future for humanity when we begin to free ourselves from the tyranny of genes.
I'd personally like to treat the Replicants as humans =) (Blade Runner reference, for those unfamiliar with it). P1 protects all similar hypothetical beings - replicants, advanced A.I.s, gene splicers that began as genetic humans, cyborgs, and so on.
So... yes, if Klingons possess and exercise the ability to declare humanity, then they must be considered human. Note, however, that if 'being Klingon' and 'being Humans' are, by definition, contradictory, then P3 is violated, and all associated assertions ('I am a Klingon', 'I am a human', 'A Klingon is never a human; a human is never a Klingon') are rendered moot.
A similar example was given in my previous post:
If an AI were to achieve human-level consciousness, and declares itself human, then it is human (by P1).