"It's just too convenient for people to cause mass murder right now."
We've had repeating firearms for more than a century--this is not a new thing to be afraid of.
We've been killing each other on much larger scales much more inefficiently and painfully than that--try millenia ( http://en.wikipedia.org/wiki/Nika_riots ).
The problem is not inefficient killing. The Rwandan genocide was performed largely without firearms, but required massive planning and mobilization. It was a collective and political massacre involving the complicity of many.
The problem I have is with the proverbial army of one. It needs to be harder for a single person to murder 30 people in one incident.
We've had repeating firearms for more than a century--this is not a new thing to be afraid of.
We've been killing each other on much larger scales much more inefficiently and painfully than that--try millenia ( http://en.wikipedia.org/wiki/Nika_riots ).