The rationale for the constitutional right to bear arms was the need to be able to raise a well-armed militia against foreign armies. The arms even in the USA in private hands are a broken reed in any military conflict in today's world.

No, it wasn't. Read the quotes I included above. It was to protect the people from their own government.

As for "arms...in private hands" -- the Vietnamese vs. the French and later the Americans, the Afghans vs. the Russians, the Zionists vs. the British, the Libyans vs. their government, the Syrians vs. their government, the French Revolution, the 1916 Easter Rising, the revolts of 1848 and many more incidents give lie to that thought. A person with a rifle CAN stop a tank, a person with a handgun CAN take out a helicopter. Hell, if you know how (and the information is out there) you can do either simply by using your brain. No rational person is going to use nukes or nerve gas on their own citizens.