It is a statement of a goal, or a primary reason for, the operative words/phrases which follow it...a NON-EXCLUSIVE goal or reason, as well understood by the drafters of the Constitution and the BOR.
That is, after all, the essence of your problem with the individual rights interpretation (i.e. the standard model) of the 2nd Amendment - you think the preamble is exclusive, and most on FR disagree with you.
Let's think about this - why would the drafters of the 2nd put into the BOR an amendment that only enables the government to determine who gets guns, in light of the then-recent history of the nation? After all, every single militia statute of the time assumed that the members of the militia would come bearing their own weapons - but no one EVER anticipated taking those weapons away when the militiaman got too old (for example, at age 45 if the militia in that state was all males at least 18 years old and under 45 years old). No one ever conceived of taking away the rifle of a 16-year-old, even though he was too young to officially be subject to call-up to the militia. Also, how was a militiaman to become familiar with, or even good at, using his firearm if the only time you could own a firearm was while serving in the militia (or while of militia age)? People then learned at a very young age how to use weapons. People then who were older than 45 taught their young kids or grandkids (both younger than and of militia age) how to use weapons - but if they were barred from owning weapons because they were too young or old, then how could they do this?
If you think that this last paragraph is entirely nonsensical, then think about what your interpretation of the 2nd Amendment would be if the Congress passed legislation, signed into law by the President, defining the militia as "all males between the age of 18 years and 18 years and 3 days of age who are not on active duty in the armed forces." I see no legal reason why the Congress and President couldn't pass such a law - as stupid as it sounds - and, thus, according to your view of the preamble's effect, NO ONE outside of that absurdly small age group would have any right to keep or bear any firearms. Couple that with a draft which is effective at at 18, and you will have completely eliminated all of the militia by the stroke of a pen. Do you seriously believe that this is what the drafters of the 2nd Amendment intended?
Just in case you don't follow the reasoning above, let's look at other preambles in the same document for guidance:
First, the Preamble to the Constitution itself. It sets out, in very general terms, the purpose of the Constitution. Yet, it has NEVER been considered to be a statement of any law - it is just some (very worthy) goals, which are fleshed out in the operative Articles following it. NOTHING in the Preamble will ever be used to invalidate or limit the operative text which follows.
Article 1, Section 8 - among the many powers of the Legislative Branch is the following:
"To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries;" [emphasis added]
"To promote the progress of science and useful arts..." is the preamble in this clause. It is more similar to the preamble of the 2nd Amendment than the Preamble to the Constitution, since it is part of the same sentence, but the effect and meaning is the same: to state a goal, a primary purpose. However, even if it could be argued successfully in court that a particular book or invention DIDN'T "promote the progress of science and useful arts," the power vested in Congress to grant copyrights and patents WOULD STILL EXIST. In other words, the preamble to this clause is not operative law, it is not capable of eliminating or limiting the powers which follow in the actual operative clause.
Such is also the case in the 2nd Amendment. In fact, I would argue that this is MORE the case with the specifically reserved rights spelled out in the BOR, since it is in keeping with the spirit of the Constitution (and its letter, see below) - which is to create the minimum government needed to avoid chaos, in order to maximize the liberties of the people.
Further, let's look at 2 other Amendments:
Amendment IX
The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.
Amendment X
The powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people.
Amendment 9 seems very clear - the societal understanding of the times in which both it and the 2nd Amendment were written was that each person had the right to keep and bear arms. [Oh, BTW, don't give me your usual nonsense about non-whites and women not having the same rights - it is inapplicable here - if I, a white male, were a DC resident, I would currently be suffering under the handgun ban at issue in Heller]. The fact that it wasn't specifically delegated to the people in Amendment 2 doesn't mean that such rights could be denied or disparaged. Amendment 10 is also clear (even though it has been widely ignored - such a state of affairs is legally absurd, as all of the words in the Constitution are presumed to have meaning): Since the United States does not have the power delegated to it in the body of the Constitution to ban firearms (whether useful to the militia or not), then such power is reserved to the states or the people. The question of state bans on firearms (i.e. the incorporation of the 2nd Amendment via the 14th) is a question for another day - but as to the federal government, the answer is clear as day: no bans are permitted, period.
Put another way:
The operative clause protects the right to individually-owned arms.
The preamble answers the common question “does that include military-specific arms like full-auto and howitzers?” with “yes, the right includes everything a well-functioning militia needs to protect the country.”
Ah. A primary reason. But one of many reasons. Could be anything. Actually, it has to be anything beause a preamble cannot limit.
Fine. So guns are protected for hunting also. Then why were guns only protected for "the people" and not all persons or all citizens? I mean, what's wrong with a 12-year-old, or a woman, or a slave, or an Indian or a non-citizen using a gun to hunt? Or for target practice? Or self-defense?
WHY RESTRICT THE RIGHT TO CERTAIN PERSONS?
"To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries;"
If you wish to compare this to the second amendment (while maintaining Miller), it would have to read, "To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries in the areas of science and the useful arts.
Awkward, but it's your analogy.