I believe the term can be justly applied, though not exclusively so, to human organisms with: properly functioning brains demonstrating sentience, brains without detectable pathology that for some unknown reason do not demonstrate sentience (e.g. some comatose patients), brains with pathology from which there is at least some hope of recovery, and fetal brains with measurable dream-like states (which happens fairly early, I think around 14 weeks, but don't quote me on that.)
It is and it isn't. But saying that 'person' is a legal term doesn't really tell me the difference between a human being and a person.
Main Entry: per·son
Pronunciation: 'p&r-s&n
Function: noun
Etymology: Middle English, from Old French persone, from Latin persona actor's mask, character in a play, person, probably from Etruscan phersu mask, from Greek prosOpa, plural of prosOpon face, mask -- more at PROSOPOPOEIA
Date: 13th century
1 : HUMAN, INDIVIDUAL -- sometimes used in combination especially by those who prefer to avoid man in compounds applicable to both sexes <chairperson> <spokesperson>
2 : a character or part in or as if in a play : GUISE
3 a : one of the three modes of being in the Trinitarian Godhead as understood by Christians b : the unitary personality of Christ that unites the divine and human natures
4 a archaic : bodily appearance b : the body of a human being; also : the body and clothing <unlawful search of the person>
5 : the personality of a human being : SELF
6 : one (as a human being, a partnership, or a corporation) that is recognized by law as the subject of rights and duties
7 : reference of a segment of discourse to the speaker, to one spoken to, or to one spoken of as indicated by means of certain pronouns or in many languages by verb inflection
- per·son·hood /-"hud/ noun
- in person : in one's bodily presence
...the term can be justly applied, though not exclusively so, to human organisms with: properly functioning brains demonstrating sentience, brains without detectable pathology that for some unknown reason do not demonstrate sentience (e.g. some comatose patients), brains with pathology from which there is at least some hope of recovery, and fetal brains with measurable dream-like states (which happens fairly early, I think around 14 weeks...
When you say the statement of the doctor regarding personhood is not science, it should also be noted that your distinction between human being and person, and your criteria for applying the distinction is not science either.
As you can see from the dictionary definitions above, person is synonomous with human and individual. Usage four in the dictionary above is classified as "archaic", but I cannot find any debate about the distinction between human being and person that is older than about 30 years (and you and I both know the reason for that.) In fact that usage is still present in both common and legal language today in reference to: bodily appearance, or the body of a human being.
I do not see any ontological basis for the distinction, simply because human beings are persons. Humans are personal beings. That's just the kind of being humans are. Personhood is not some separate, added quality - it is a property that is part of the essence of being human. For example, an essential part of being a cube is to have volume. A cube without volume is not a cube but a square. All cubes have volume. In the same way part of what being human entails is being a personal being, no matter at what particular stage of development a human being happens to be.
So if you are advancing the notion that there is a difference between human being and person, then it is up to you to justify the distinction and its logical corollary that there exists such a thing as a human being who is not a person.
Cordially