One fact is made abundantly clear by the events of Columbine, Aurora, Sandy Hook, Boston, Santa Monica, and now Isla Vista. Anyone bent on wrecking havoc in this country is free to do so with impunity; there is zero risk of return fire. The shooter can go where he wants, do what he wants, always in complete control of the situation.
Until there is reason for an attacker to fear that someone else may be able to upset the scenario the attacker has envisioned, these events will continue, probably at an accelerated rate.
Think about it.