That said, i'm not for selling civilians assault rifles or sub-machine guns. That's overkill. It's completely unnecessary.
It may be overkill, but they are fun as hell. Like fireworks, sports cars, and speed boats... it's the overkill that makes them unique and fun. If we lived in "that" world you describe we may as well get rid of mansions, Lamborghini, Corvettes, private jets and all the other things that make living worth overdoing.
I'm not opposed to facillities where you could fire those types of weapons, i'm just against ownership of them.
I also think that you're making a HUGE jump. Mansions aren't made for the express purpose of being a great killing machine. You don't need an assault rifle for hunting,and you don't need one for home-defense. You shouldn't be trying to kill someone who breaks into your home, just subdue them. I'm not saying that if you kill them, you should be tried for murder, but it shouldn't be your goal.
But you can most definitely kill someone with a huge truck, fast car, collector sword, sling shot, etc... Hell, a sniper rifle is probably the most lethal long range weapon in the world, and they are used for hunting. While you don't need an assault rifle for hunting, you also don't need dynamite to take down a concrete wall. So you are exclusively selecting guns as the target (/rimshot) for some glorification of authoritarianism. My point is, where does it stop? We are given explicit rights to own arms for purpose of forming a militia.
A well regulated militia being necessary to the security of a free State, the right of the People to keep and bear arms shall not be infringed.
It doesn't say such arms are to be used only for self/home defense. The Founders knew that the people should be able (at any time) to overthrow the sitting elected officials.
Here's a question for you. Let's say the people of this country can't get the government to cease a total takeover of everything. One day they collude together to remove the right to vote and they succeed at turning our country into an oligarchy, controlled by a "few" elite families. Now that they have control over the military who are trained to execute anyone without question using assault rifles, on order, how do you defend yourself against this?
I'm not saying it will, but as soon as you eliminate the ability to defend yourself against ANY threat, that threat becomes more and more possible.
I personally believe people should be able to own a tank if they have the means. Using such a machine against someone aggressively is fully illegal of course, but there should be no law prohibiting ownership.
edit: Also, how do you now describe an assault rifle? Is it something that fires so many rounds per second? Does the barrel have to be of a certain length? As soon as those laws are set, someone comes along and makes a gun that just barely doesn't fit into that description just to make it legal. In order to classify weaponry, you'd have to "nascar"ify the entire weapon market by placing strict controls over size, shape, color, shell, etc. It's literally not possible.
Second edit (sorry): Me and my brother were out shooting his AR-15 (ZOMG, assault rifle! Look it's in the name!... even though it's gimped by not making it automatic switchable) and we saw a ground hog out in the field. My brother didn't go run and grab another rifle from the safe. He crouched down, sighted in and shot it at 150 yards. So in essence, he was hunting with his assault rifle.