I agree... but to be honest, I think it's ok to regulate what arms can be privately owned.
If you want to really go down the rabbit hole then it would be possible for there to be private armies with tanks and war planes. I have watched to many movies too think it's a good idea for Google (or some corporation) to have an army. Serious. If you allow private citizens to have tanks it'd be tough to stop private entities to have them in mass.
Lots of private entities have tanks, planes, artillery, etc. None of these are illegal to own if you have enough money.
One of the founders of Microsoft has a WWII addiction, and he has fully operational version of all the above, plus machine guns, grenades and all the non-NFA stuff.
Or go down to World of Tanks down in Texas sometime. Those aren't decommissioned, most are fully functional.
The simple fact is that to own heavy weaponry you just have to be rich enough to afford the price tag, including the legal costs.
