So where does that leave non-firearms related weapons? Potassium nitrate bombs are easy to make and can result in far more deaths than guns can. You can make napalm by soaking styrofoam in gasoline. Should we control the usage and distribution of packing peanuts? It may sound like a ridiculous argument, but it's the exact one you're making. What about machetes or hunting knives?

If the real focus is to inflict mass casualties, there are tools far more appropriate for that sort of thing than guns and non-automatic rifles that take as much (or as little) planning as getting a hold of a gun and ammo.

As someone else already said on this thread: you can't ban mental illness with legislation.