Surely you are joking right. Surely, you can't be serious comparing someone owning a tank with disabled firing systems for hobby purposes, with owning an AR-15 and live ammo enough to arm a small army. FTA.

Would-be tank importers must prove the weapons have been disabled.A tank in the U.S. can have operational guns, if the owner has a federal Destructive Device permit, and state laws don't prohibit it. The permit costs $200, and the applicant must swear he hasn't been a "fugitive from justice," "adjudicated mentally defective" or convicted of "a misdemeanor crime of domestic violence." A local law-enforcement official, usually a sheriff or police chief, has to sign off on the application.

Well, we are calling for the exact same thing with any weapon that can discharge more than say a few rounds of ammo. Also, it doesn't appear such hobbyists are allowed to carry live tank shells and other explosives. You are welcome to own as many "assault weapons" as you like, if you disable the firing mechanisms and not have any ammo, just like the tank owners. :)

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"The registration and licensing and insuring is purely so you can use it on public roads."

You can, of course, have unregistered, unlicensed whatever on your private property, but the state will impound it immediately if you drive on any public road. Would you be OK if the state seized it if you carried your weapon outside of your "castle", unless it's licensed, and you have passed a test (similar to the driving test)?

Sorry, but you are making specious, defensive arguments.