I can own a bazooka as long as I register it and pay the taxes on it. Is it wise for me to own a bazooka? That's a different question. IMO it is the same as being able to buy a car that can go over 200 MPH. Do you "need" a car that goes that fast? No. Can you legally own a car that goes that fast? Yes.
A state can decide which cars are street legal. Many high performance cars are not
Same goes for guns
The OP question began "Should Americans be allowed to own...". A state's authority to ban certain cars and certain guns is not relevant to that question. I personally don't understand why Americans want to own ultra fast cars and ultra powerful guns but this is America. Own what you want but you are responsible.
Not really. Goober Gump's net worth, including his underwear and half a tube of Vaseline gel, is $24.45. He's drunk as usual on Saturday morning, after his 10 breakfast beers, and accidentally sets off his military surplus 20kton warhead in his garage he bought through an ad in the back of Popular Mechanics. He didn't do it on purpose, he's a good ole boy and all that.
You think Good ole Goober's estate will cover the damage and revive the victims?