Why not? "The right of the people to hold and bear arms shall not be infringed -- never mind why, we just threw that in to give you a hint about our intent." Why is that not the correct understanding of the operative clause?
Well, obviously, some people do
interpret the prefatory clause in that fashion. Five of them happen to be on the supreme court.
On what principle of statutory construction do you conclude that the prefatory clause isn't just another one of those barely consequential "whereas" clauses?
Because the prefatory clause isn't a "whereas clause." A "whereas clause" is like the preamble to the constitution, which talks about "forming a more perfect union" and all that stuff. Nobody reads congress's powers under article I as being constrained by the preamble (well, there probably are
such people -- there are all kinds of constitution nuts
out there). Nobody says "congress only has the power to establish post roads so long as they lead to a more perfect union." That would be to misunderstand the nature of a preamble, which is meant simply to set forth broad principles rather than modify the operative sections of the constitution.
The prefatory clause of the second amendment, on the other hand, is meant to be read along with the operative clause -- they're in the same sentence. There's no rule of statutory construction that allows a judge to read part of a sentence and disregard another part. Indeed, the rule of construction is to give effect to all
parts of a law. "[C]ourts should disfavor interpretations of statutes that render language superfluous" said one eminent jurist
So far, your reasoning sounds circular to me: The court got it wrong because it ignored the prefatory clause. And it shouldn't have ignored the prefatory clause because the operative clause can't be correctly understood without it.
If my reasoning sounds circular to you, then you might want to get your hearing checked.
I do find your argument persuasive, though, when you apply it to the copyright clause. "Congress shall have the power to promote the progress of science and useful arts, and here's how ..." is not the same as "congress shall have the power to secure for limited times to authors and inventors the exclusive right to their respective writings and discoveries, never mind what for."
I don't know why one prefatory clause modifies the operative clause and the other one doesn't. What if the copyright clause had been written thus:
"Because promoting the Progress of Science and useful Arts is a good thing, congress shall have the power to secure for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries."
Wouldn't that say the same thing? And if so, how is that different from the way the second amendment is written?