y. Hand grenades would not be prohibitively expensive if a general market existed, nor would fully automatic weapons, C-4, mortars, or mustard gas for that matter.
And why should the law abiding civilian population not be permitted to possess these items? (The cynical side of me secretly thinks it's a good idea based on it will further human evolution)
Re: Mustard Gas - a few household chemicals and a bit of chemistry know how and you can make your own small scale chemical weapons ("Mustard gas" can
be home made), even to the point of incendiaries and aerosols. It is easier to obtain legally than high explosive destructive devices per the NFA.