So says the Washington Supreme Court, State v. Williams, 2006 WL 3438188 (decided yesterday), and uses this as a justification for interpreting a state ban on possessing short-barreled shotguns as requiring knowledge that the shotgun was indeed shorter than the statutory limit. Here's the relevant excerpt from the three-Justice plurality:

[W]e are ... concerned that possessing a firearm can be innocent conduct. Citizens have a constitutional right to bear arms under both the federal and state constitutions. U.S. Const. amend. II; Wash. Const. art. I, § 24. A person may lawfully own a shotgun so long as the barrel length is more than 18 inches in length and has an overall length of less than 26 inches. RCW 9.41.190 precludes possession of a short-barreled shotgun. Moreover, the statute also criminalizes possession of a short-barreled rifle and a machine gun. The factor concerned with innocent conduct is particularly important in the case of a machine gun, which can be altered in ways not easily observable. If strict liability is imposed, a person could innocently come into the possession of a shotgun, rifle, or weapon meeting the definition of a machine gun but then be subject to imprisonment, despite ignorance of the gun's characteristics, if the barrel turns out to be shorter than allowed by law or the weapon has been altered, making it a machine gun. The legislature likely did not intend to imprison persons for such seemingly innocent conduct.

The four-Justice dissent agrees entirely on this point:

These holdings involve a particularly sensitive and limited area of regulation, since both the United States and Washington State Constitutions protect a "right ... to bear arms ...." U.S. Const. amend. II; Wash. Const. art. I, § 24.... The majority's recognition that the State must prove a defendant knows the characteristics that make a firearm illegal means that knowledge of the characteristics that make the firearm illegal is an essential element of the crime....

The plurality and the dissent disagree on whether the failure to instruct the jury about the defendant's required mental state was harmless in this case, but they agree that the Second Amendment protects the right to bear arms, and that this counsels against reading the statute as imposing strict liability.

As you can see, neither opinion explained much about why it was accepting the individual rights view of the Second Amendment, but just cited the Second Amendment and the Washington right-to-bear-arms provision.

UPDATE: I originally quoted the plurality without noting that it was a plurality, and didn't mention the dissent; my mistake — thanks to commenter marksleen for pointing out. I've corrected the post accordingly, and the bottom-line remains the same: A majority of the Washington Supreme Court treated the Second Amendment as securing an individual right to bear arms.