Argh... post accidentally deleted...
Many apologies, clo - I tried to re-create my inadvertantly deleted post. If I have changed any salient point with which you have issue, please let me know.
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There is NO REASON a civilian needs an assault rifle, NONE!
What is it, in your opinion, that makes an 'assault rifle,' as defined by the media and the average person, more dangerous than a non-assault rifle?
A true assault rifle is one that supports fully-automatic fire - multiple shots fired with each trigger pull. That's what the military uses. The civilian ownership of such weapons has been heavily restricted and regulated since 1934, and while civilian ownership of such weapons is legal in some states, it takes a special license, many months of ATF paperwork and red tape, and a LOT of money.
What most people call an 'assault rifle' nowadays is something that LOOKS like it could fire in full-auto mode - but it does not. The AR-15s and such that are commercially available on the civilian market are semi-automatic firearms - one shot per trigger pull.
Take the Ruger Mini-14, for example - a popular small-game hunting rifle. The basic version has a simple wood stock, and it can be easily adapted to handle a scope. Now take that same gun, and swap out the wood stock for an adjustable one (one would do this so two different-sized shooters - say, a husband and wife - can safely and comfortable shoot with it), and put on a flash-hider (which minimizes the muzzle flash when firing, to protect the shooter's eyes when firing in low-light conditions, such as hunting predators threatening livestock at night) - and voila! - you have an assault rifle. Same barrel, same trigger, same caliber, still semi-automatic. Only the safety/cosmetic features have changed. Why should those safety features not be available to the civilian hunter?
I do realize, of course, that from a distance, you can't tell what type of gun the person has, and police will probably assume the worst case scenario.
It was reported he had a clip that held 100 rounds, again NO REASON a civilian needs that! NONE!
Then what would your arbitrary limit on magazine capacity be? I say arbitrary because no matter what number you choose, it will end up being one too many at some point. If you limit magazine capacities to 10 rounds, for example, all one would need to do is carry multiple magazines, or a "New York reload" - multiple guns.
Large capacity magazines, such as the 31-round magazines the Arizona shooter used, have a greater tendency to jam and high failure rate. In fact, with smaller magazines and/or additional firearms, he might well have caused more damage than he did. After emptying his first magazine, he reloaded with the second - and it jammed. That delay allowed the crowd to subdue him.
I personally don't like high-capacity magazines like the 31-rounder for anything but target shooting, due to the various problems they have. When I go to the range, I'm paying by the hour, thus I don't want to spend my time loading magazines. I would never carry (or hunt with) such a magazine. For those purposes, I'll stick with the magazine for which the gun was designed.
What is the point of rules that are not enforced?