Lacking a definitive RULING by the USSC (US Supreme Court) on this specific issue....your point is invalid. Past holdings tend to support your theory (which I too subscribe to--but I'm also a realist, which is not your strong suit) but nothing since 1935 which we technically lost in the US v Miller case. The 2nd Amendment (don't quote it to me...I have it memorized and I teach Honors American Government) is still open to interpretation by the states and the USSC has not yet struck down any of the blatantly unconstitutional gun laws passed in the last 50 years based on YOUR interpretation of the Amendment. I'll say it again: GET REAL and deal with the issue based on the paradigm of the current playing field.
I'll say this: If the next terrorist attack is aborted by a LAWFULLY armed citizen, the paradigm will take a dramatic shift back to the vision of the Founding Fathers.