The question in 1788 was not whether Americans needed arms. It was who would hold them.
At Virginia’s ratifying convention, Patrick Henry refused to treat congressional management as the same thing as the people keeping their own arms:
“Are we at last brought to such a humiliating and debasing degradation, that we cannot be trusted with arms for our own defence? Where is the difference between having our arms in our possession and under our own direction, and having them under the management of Congress? If our defence be the real object of having those arms, in whose hands can they be trusted with more propriety, or equal safety to us, as in our own hands?”
— Patrick Henry, Virginia Ratifying Convention, June 1788 (3 Elliot’s Debates 386)
If defense is the reason, the people’s own hands are the safest place for those arms.