I'm on a tangent here, but this is relevant to the terrible civics education in our country.
The Bill of Rights doesn't empower anyone to do anything. None of us have affirmative Constitutional rights empowering us to speak freely, to dissent politically, to assemble, to practice religion, or to bear arms for self defense.
The Bill of Rights commands the government to respect innate human rights by not imposing arbitrary limits on them. The First Amendment doesn't say "citizen, you can speak!" -- it says Congress shall pass no law abridging the freedom to speak. The Second Amendment doesn't give us a right to bear arms of any kind, it says Congress shall not infringe the right to protect ourselves and our communities with arms.
The Bill of Rights are explicit limits on government that were the conditions precedent for the ratification of the Constitution.
So, it's not really a "Bill of Rights versus Bill of Needs" issue. Your ability to possess an AR is not granted by the Bill of Rights, or even relevant to it. If we abolish the First or Second Amendment, God forbid, your rights as a human being don't change.
You have a natural human right to protect your family and your neighbors from being rounded up like the Japanese in the 40s, and you have a right to repel and abolish any government that would attempt to do the same with effective bearable arms.
ETA: So, I guess the proper response to "you don't need that AR" is, "Someday I might. Someday you might. And, the government is constitutionally barred from deciding otherwise."