It can, and reduce the amount of fully automatic rifles easily available, which is a major factor......There's a wide margin of difference between arms traffickers smuggling in crates of rifles (which is borderline absurd anyway) mass killers buying on the black market, and walking into a Wal Mart around the corner, or a gun show. James Holmes the goofball from Aurora is not going to purchase an AR-15 from a black market arms dealer in a van in front of a Burger King. Nor is the Sandy Hook kid. They all had easy access to legally purchased automatic/semi automatic rifles. But, hundreds have to die every year, so hunters and gun freaks can feel comfortable from their rural or suburban existence, where they imagine they are knee deep in Juarez drug wars or whatever.
I saw in my local paper there were off duty SDPD there, (figures redneck country shyt) I wonder why they weren't able to disarm and kill the shooter before all these bodies piled up.
Because, an unpredictable gunman, firing from cover, and a vantage point would be fukking impossible to stop with anything but a sniper team, or a SWAT team.