The Indian Citizenship Act granted citizenship to Indians. Pretty clearly allowed under the naturalization power of Congress.
Getting rid of birthright citizenship would arguably conflict with the wording of 14A and therefore require an amendment.
You cannot argue that it wouldn’t be litigated and require a Supreme Court decision. They would have to decide if 14A grants birthright citizenship or not. If it doesn’t, they Congress can just pass a law. If 14A does grant citizenship by birthright, then it would require an amendment to repeal it.
AFAIK, it’s pretty clear by Wong Kim Ark that 14A gives birthright citizenship to children of legal residents. Children of tourists and of illegal aliens AFAIK the Supremes have never ruled on.
Well there’s that pesky clause of 14A....and subject to the jurisdiction thereof....
I would argue that that’s plain language that foreign nationals are not subject to the jurisdiction of the US...and were never intended to be covered by 14A.
That’s where I think Congress can legitimately clarify this by statute. Would it be challenged? Of course. But at that point we will have clarification one way or another.
And BTW, IIRC children of foreign diplomats born here do not have automatic American birthright citizenship.