You could do worse than to read this elegant critique by Jack Balkin of Scalia’s opinion.

And here is the point: The argument that the Second Amendment constitutionalized the right of self-defense does not follow directly from the Amendment’s original meaning, as Scalia claims it does. Just because a reading is consistent with original meaning, that does not mean that it is required by original meaning.

Rather, it is a permissible construction or gloss on the Amendment. It is a gloss that develops over time, and becomes generally and widely accepted by Reconstruction, and continues throughout the 19th century, as Scalia’s opinion suggests. However, because Scalia wants to insist that this was always an original purpose of the Amendment, he reads this 19th century history as proof of the original purposes of 1791. This is anachronistic. And, as noted above, he confuses original meaning – i.e., the content of the words used – with original purpose and original expectations.