...regarding the police chiefs out there (who, we are told, have come out against the Second Amendment): Every law enforcement officer is required to take an Oath, affirming said officer's commitment to the Constitution of the United States.  Here is one example taken at random.  I'm sure you can find many others:

“I swear (or affirm) that I will support the Constitution of the United States, and that I will be faithful and bear true allegiance to the State of Maryland and support the Constitution and laws thereof; and that I will, to the best of my skill and judgment diligently and faithfully, without partiality or prejudice, execute the office of police officer according to the Constitution and laws of this State.”

Notice the first clause-- support for the U.S. Constitution.  Taking an Oath not only suggests or recommends, but it requires individual judgment and individual commitment to the U.S. Constitution when deciding to follow a particular order or enforce a particular law.  It requires, in this case, that the sworn individual understand the Constitutionality of an action before taking that action.  Why else take the damned Oath?

The Nuremburg defense doesn't cut it here.

On the matter of law enforcement officers who have taken the Oath, and who then actively lobby against our Constitutionally protected civil liberties:  Words fail me at the moment, but I'm envisioning a physician who takes the Hippocratic Oath and sets out thereafter to murder his patients.

To you chiefs of police out there who are on the fence:  Be reminded that some of us actually take our civil liberties seriously.  Just sayin'.

Update 09/21/07:  Another reminder for our friends in law enforcement (and to law makers as well).  I use this example only because it is so well known, though there are plenty of other examples: In early 1942 there were a whole lot of German officers and government agents who were as cock-sure of themselves as anyone could be.  Their degree of swagger was quite an impressive sight to behold.  Only a few years later however, many of them were fugitives from justice, while others were swinging from ropes (things can change in short order, and being on the right side of Liberty is good insurance).  As Joe points out in comments, there is this little thingy we call 18 USC 242.  Not that it would be needed as the Constitution already spells out the law in plain English, but here we have teeth, out in front of the brain, as it were.