Quoted:
There are those on the left who believe the Constitution and Bill of Rights are living documents and are open to [interpretation].
It's not the Constitution that changes, it's us.
Rather than being a "living document" that can be reinterpreted to suit the whim of current political theories, the Constitution contains many unchanging fundamental principles that must be applied to new or changing situations.
When I argue that a constitution that can be constantly reinterpreted is worthless because it ceases to have meaning, the "living document" people almost always bring up the example of the Constitution being "reinterpreted" to deal with the issue of slavery. I point out that the basic concept didn't change - the right of the people to be free didn't change, Congress merely expanded the definition of "people" to include former slaves.
Thus, the 2nd Amendment isn't obsolete because there aren't many local militias around today, it just has to be applied in a way relevant to our current situation. Maybe the Founding Fathers didn't envision Glocks, but they didn't envision illegal immigration, domestic terrorism, crack, or gang warfare, either.
The 1st Amendment was applied by analogy to the electronic media, there's no reason the 2nd can't be applied to our current situation in a similarly valid way - no reinterpretation necessary.