Why allow the dangers inherent to the one when the other will suit any reasonable purpose? I'm originally from Long Island, exemplar of suburbia, but I spent a significant portion of my youth living in upstate New York, where hunting is a way of life. I've done a lot of target shooting with a wide variety of single-shot weapons; my brother is an avid hunter of deer and turkey. I don't have a problem with people owning a Browning .308 (which my brother owns and I've shot) because it's a reasonable weapon for hunting deer, although it can be used for more nefarious purposes. I don't have a problem with people owning a Remington 870 (which, believe it or not, I shot at summer camp as a 13-year-old) because it's a reasonable weapon for hunting bird, although it too can be used for more nefarious purposes. I do however have a problem with someone owning a Bushmaster .223 or an AR-15, because they're primarily designed for one purpose and it's not hunting rabbits.
Out of curiosity, I just Googled "Bushmaster .223" and the link below is the second result that came up. You can mail-order an entire freaking armory. If you browse around the site, you'll find the seller's Conditions page, where he essentially offloads all responsibility for the purchase being legal to the buyer. He even provides a "cash discount" for purchasing with something other than a credit card. I won't fault him too much, as it's not his fault all that stuff is allowed. But isn't that at least a little concerning? I don't mean to focus in on this one guy too much - the point is more that if I can find this site as the second result in a Google search for a particular weapon, how hard could it really be for someone to stock up on weapons that no civilian would ever need unless Red Dawn actually comes to pass?
It's frighteningly easy to get weapons of mass murder that have no business being available on the open market. And that's not even getting into strawman purchases, gun show purchases, the ridiculously wide chasm between strictness of different states' gun laws, etc.