One of these things...

It's interesting to look at the U.S. Constitution and the Bill of Rights with a Sesame Street song stuck in your head: "one of these things is not like the others, one of these things just doesn't belong."  OK, kind of a strange thought for a legal document, but stick with me for a moment.

The Preamble provides the justification for the Constitution:

• We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.

It's pretty clear that the preamble doesn't set any particular laws or duties for the government, but instead provides a statement of why the Constitution was written and the intent of those ratifying it.

If you peruse the documents for other justifications, you'll find only one. Outside of this single exception, the Constitution and Bill of Rights below the Preamble is simply a declarative list of the duties and limitation for each branch of government.  None of the provisions have any justification, except...

• A well regulated Militia, being necessary to the security of a free State....

What's up with this justifying phrase in the 2nd Amendment?  No where else in the Constitution or the Bill of Rights is there any reason given for any provision.  Why does this Amendment need a justification while others do not?

The 1st Amendment could have been written as...

• Freedom of thought and communication are necessary for a free State, so Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.

... but it wasn't.

The 2nd Amendment could have been written as

• The right of the people to keep and bear Arms, shall not be infringed.

.. but it wasn't.

Didn't our founding fathers notice a justifying phrase in their otherwise pristine declarative laws? Were they just slipshod in their writing? Or is there meaning in this Amendment having a justification absent from all the others?