The government's own lawyers argued before the SCOTUS that
http://en.wikipedia.org/wiki/United_States_v._Miller said:
1. The NFA is intended as a revenue-collecting measure and therefore within the authority of the Department of the Treasury.
2. The defendants transported the shotgun from Oklahoma to Arkansas, and therefore used it in interstate commerce.
3. The Second Amendment protects only the ownership of military-type weapons appropriate for use in an organized militia.
4. The "double barrel 12-gauge Stevens shotgun having a barrel less than 18 inches in length, bearing identification number 76230" was never used in any militia organization.
No expert witnesses bothered to show up and inform the Justices that the Army did indeed use a shotgun with a barrel less than 18 inches, so Miller was convicted. However the government's own lawyers essentially argued that I should be allowed to own a MP5SD, M4A1, M249, M240L, Mk46, Mk48, Mk16, Mk17, and so on.
That quiz mentioned United States v Miller but apparently they didn't read the full background of the decision.
US code also states that all males between the ages of 17 and 45 are members of the unorganized militia (
http://uscode.house.gov/download/pls/10C13.txt), so even if you subscribe to the "only the militia can have guns" viewpoint you're basically saying all males 17 - 45 can own a MP5SD, M4A1, M249, M240L, Mk46, Mk48, Mk16, Mk17, and so on.
But hey, I got 11 of 12 right on their quiz, and the one I missed was their opinion question.