So, Blackstone doesn't help you any.
From Blackstone's Commentaries:
When I say, that an alien is one who is born out of the king's dominions, or allegiance, this also must be understood with some restrictions. The common law indeed stood absolutely so; with only a very few exceptions: so that a particular act of parliament became necessary after the restoration, for the naturalization of children of his majesty's English subjects, born in foreign countries during the late troubles. And this maxim of the law proceeded upon a general principle, that every man owes natural allegiance where he is born, and cannot owe two such allegiances, or serve two masters, at once. Yet the children of the king's embassadors born abroad were always held to be natural subjects: for as the father, though in a foreign country, owes not even a local allegiance to the prince to whom he is sent; so, with regard to the son also, he was held (by a kind of postliminium) to be born under the king of England's allegiance, represented by his father, the embassador. To encourage also foreign commerce, it was enacted by statute 25 Edw. III. st. 2. that all children born abroad, provided both their parents were at the time of the birth in allegiance to the king, and the mother had passed the seas by her husband's consent, might inherit as if born in England: and accordingly it hath been so adjudged in behalf of merchants. But by several more modern statutes these restrictions are still farther taken off: so that all children, born out of the king's ligeance, whose fathers were natural-born subjects, are now natural-born subjects themselves, to all intents and purposes, without any exception; unless their said fathers were attainted, or banished beyond sea, for high treason; or were then in the service of a prince at enmity with Great Britain.
First off - there are no British "citizens". They are all subjects of the crown.
They key sentence in the Blackstone quote you posted is:
" But by several more modern statutes these restrictions are still farther taken off: "
No law enacted by man can supersede the Laws of Nature. So in essence the British crown enacted a form of naturalization at birth statute.
This is similar to what happened with our own Naturalization act of 1790. Which was soon after corrected with the Naturalization act of 1795:
The United States Naturalization Act of January 29, 1795 (1 Stat. 414) repealed and replaced the Naturalization Act of 1790. The 1795 Act differed from the 1790 Act by increasing the period of required residence from two to five years in the United States, by introducing the Declaration of Intention requirement, or "first papers", which created a two-step naturalization process, and by conferring the status of citizen and not natural born citizen.
xzins: “Blackstone himself supported the blood-based citizenship of children born overseas to British citizens.”
I’m on the fence on this topic but there is an obvious contradiction I see in your argument.
If, as you suggest, a citizen gives birth to a child in a territory that is not native to that citizen and the resulting child maintains the nationality of the citizen parent, how does that work when the other parent is of different nationality? Especially when the other parent’s nationality is the same as the place of birth? Doesn’t this demand some priority placed upon how nationality is conferred? Perhaps the father’s nationality is of higher weight? Or the mother’s nationality (as Judaism suggests)? Or perhaps the location of birth trumps all? Is it possible that a child can be “natural born” with two different nationalities??
And as I have seen argued on these threads previously, perhaps citizen at birth can be distinguished from “natural born citizen”. Because saying someone is naturally born a dog and naturally born a cat at the same time seems ludicrous.