Why not? Do you think they'd shoot it at you? Do you also not want them to have a nitro jet boat, a 60' RV, or some other kind of recreational equipment?
Just because they're legally permitted to own a 60' RV doesn't mean they must be allowed to park it on the street.
In most states, your neighbor is already permitted to own a grenade launcher and 50-caliber machine gun under certain regulatory restrictions, so do you object to that particular adherence to the Constitution as well?
Because if a neighbor messes up with a 155mm shell, the whole neighborhood goes up in flames with him. Do you not understand the concept of a middle ground somewhere between total freedom (anarchy) and totalitarianism?
I’m assuming states that permit grenade launchers and 50 caliber machine guns have regulations to reduce the risk to the general population. But you either missed my point early on or are simply ignoring it.
There are people who are gun, drug and porn absolutists who tolerate no government restrictions on their liberty whatsoever. They are essentially anarchists who benefit from a stable, governed society, but don’t apparently understand one has to give something up in return for civilized society.
Then there’s this massive group of people somewhere in the middle who understand that crystal meth and 155mm howitzers shouldn’t be readily available to private citizens.
Finally, the US Constitution does not guarantee your right to get high. It’s supposed to restrain the federal government, but a state can lock you up (legitimately) if a majority of its citizens vote to ban a drug and you violate that ban.
(And I’d be one of those voting to ban it, too)