The graph is dumb anyway, if it's harder to buy a gun then you'll see less gun deaths, but that doesn't mean there will be less murderss which is the stat that matters. For instance on that graph Arkansas is the highest and California is the lowest, but California has a higher murder rate than Arkansas. Arkansas in 2010 only had 130 murders, it's just 100 of them were committed with a gun. That doesn't mean there'd be less murders if there weren't guns though.
It's a lot harder to murder someone in a moment of seeing red with bad words or flailing fists than with the weapon you happened to be legally carrying.