I'm not for banning guns (well, maybe assault weapons) but you're just trying to justify their use/existence because you want them. Nothing more.
That's just the thing. What is wrong with wanting them, or more importantly, wanting the individual liberty to have one if you so choose? And why is the first reaction to very tragic, very rare events always to trade individual liberty for what is assumed to be increased public safety?
It's a slippery slope.
At least let's get serious about assault rifles with 50 round clips, yes, you can whack someone in the head with a toaster and kill him/her or run someone over, ect, ect. Point is an assault rifle with a large clip represents the current state-of-the-art for killing mass amounts of people, if we could at least ban these it would be a start..
There are magazine capacity restrictions in many states. Such a restriction was also part of the '94 Clinton/Feinstein "Assault Weapons" ban. It really didn't do anything for violent gun crime. It was, however, a regulation which deeply affected the vitality of the American gun industry, which employs more people than you think.
To be honest, a negligible portion of gun crime (which oddly occupies 90% of the media's attention) is committed with high capacity magazines. On the other hand, gun owners enjoy the individual freedom to own and use these high capacity magazines for their own purposes. If you're actually interested in reducing violent gun crime, it is an odd place to start.
As much as some would like to believe "the only purpose of guns is to kill people" (and those people, invariably, have never used a firearm and are in general are informed about them only via TV or other media), the vast majority of legally owned firearms is used to shoot at paper and animals.