I'm going to give you a pretty full and detailed answer to that question.
Because:
1. Rawle was a major authority, not a minor authority like Samuel Roberts, who ran the Court of Common Pleas for several counties in Pennsylvania. He was an authority not only by his legal acumen, position and stature, but also by his intimate personal association with our core Founders.
2. Rawle's view is in accord with every other major authority in the early United States who speaks clearly on the subject (e.g., Joseph Story, St George Tucker)
3. Rawle's view is in accord with every other significant authority in the early United States who talks about what a natural born citizen is, or what Presidential eligibility requires (see my list of some 30 or so early American authorities and what they had to say on the subject.)
4. Rawle's view is in accord with the general principle, expressed by James Madison, that place of birth was "what applied in the United States." Not place of birth plus parentage. Place of birth. And yes, parentage helped, and parentage by itself was suffiicient to make a natural born citizen according to the first Congress, but in general, the rule was "place of birth." This was also confirmed by Thomas Jefferson's 1779 jus soli rule for the Commonwealth of Virginia.
5. The view that you (and Samuel Roberts) espouse, which is contrary to Rawle's clear statement, is not in accord with the law of early America. Nowhere in the country, as far as I have been able to determine, was there any law or tradition that said persons born of immigrant parents were anything other than natural born US citizens.
6. Rawle's view is in accord with the law of early America. I haven't posted it yet, but in looking at the laws of the Thirteen Original States, there is good evidence that every single one of them either adopted the common law of England to the extent that it did not conflict with their own newer laws, or simply continued to operate under the English charter they had been founded with.
7. The only judicial authority in early America to review the question came to the conclusion that since every State of the Union adopted the English common law, and no State issued any contrary law or ruling, the common law of England, in regard to citizenship became the common law of the United States. After an extensive review, Vice Chancellor Sandford, in Lynch v. Clarke (New York, 1844) further commented:
Suppose a person should be elected president who was native born, but of alien parents; could there be any reasonable doubt that he was eligible under the Constitution? I think not. The position would be decisive in his favor, that by the rule of the common law, in force when the Constitution was adopted, he is a citizen.
(Notice that after his extensive review of the law, he draws no real distinction between a person being a citizen at birth and being a natural born citizen.)
And further:
Upon principle, therefore, I can entertain no doubt, but that by the law of the United States, every person born within the dominions and allegiance of the United States, whatever the situation of his parents, is a natural born citizen.
8. This understanding of Sandford and Rawle was fully affirmed by the United States Supreme Court in 1898. They said that the same rule had always applied:
First in England.
Then in the American Colonies.
Then in the early United States after the Revolution.
Then in the United States after the establishment of the Constitution.
An accurate expression of that rule, as applied to the United States (and subsituting our American terms that the Supreme Court specifically told us were equivalent to the English ones) would be:
"Aliens, while residing in the dominions possessed by the United States, are within the allegiance, the obedience, the faith or loyalty, the protection, the power, the jurisdiction of the collective body of the American People, and therefore every child born in the United States, is a natural born citizen unless the child of an ambassador or other diplomatic agent of a foreign state or of an alien enemy in hostile occupation of the place where the child was born."
So we should accept Rawle's view as the standard, not because of his authority, but because it is his view that is consistent with the history and law of the Founders and the Founding Generation, as well as with the ruling of the US Supreme Court on the matter.
“1. Rawle was a major authority”
Rawle provides no authority for his definition of what is a natural born Citizen. Rawle’s claim to fame in our Supreme Court decisions is on the 2nd Amendment (the right to bear arms), not citizenship.