IF the argument had been made that the restrictions in the 1st ammendment pertained to free speech exclusively (therefor exposing the need for such an ammendment), I wonder what debate the Founding Fathers would've had regarding the nuances and subtleties respecting either of our nominations for such ammendment.
Just for arguments sake, suppose the adage: "The pen is mightier than the sword" carried significant weight, and therefor was an issue of contention.
If the second amendment stated, "A citizenry well trained in arms, being necessary to the security of a free State ....", then your comparison to a "well educated electorate" would be valid. It doesn't read that way.
The second amendment designates an institution, a Militia, that needed to be well regulated in order to be effective at securing a free state. My "library" is the Militia.
"the benefit of libaries to that of a free State is rather obtuse"
No. You've already stipulated that books are necessary to the security of a free state. And if the Founding Fathers thought that books alone would secure a free state, then there'd be no use for libraries and no need to mention libraries in an amendment.
But they felt it went beyond just books. Books needed to be available to those who didn't have them, didn't see an immediate need for them or couldn't afford them. The library would contain large books that no one would have in their home. The information needed to be organized to be effective. The state needed to appoint librarians.
My analogy holds.