Gerard Magliocca identifies an odd twist: to offer non-citizens RKBA, you have to ignore the original meaning.
One theme that emerges from an examination of John Bingham’s understanding of the Fourteenth Amendment is that: (1) he wanted the Bill of Rights to apply to the States; and (2) he thought only citizens were entitled to the protections of everything in the first eight amendments. Non-citizens were entitled to due process and equal protection, but not to something like, say, the right to bear arms. The Supreme Court, though, has completely obliterated Section One’s distinction between citizens and persons by incorporating most of the Bill of Rights through the Due Process Clause which, of course, applies to all persons.
Nevertheless, there now appears to be a movement to resurrect Bingham’s distinction as between legal residents (citizens and aliens) and illegal residents. In other words, courts seems hesitant to say that illegal aliens have, for example, a right to bear arms or certain other protections in the Bill of Rights even though the right is recognized as fundamental under the Due Process Clause.
This is the implication Justice Thomas (and Gura, et al) failed to really confront in McDonald. If the right to keep and bear arms was extended to the state through the Privileges or Immunities Clause–which applies only to citizens, not persons–then the right would not protect non-citizens (such as illegal alens).