Law enforcement, on whatever level you choose to address, has always been very ineffective in the control or banishment of any type of item or substance.
Heroin has been banned since 1924.
Cocaine has been prescription only since 1914.
Until this decade cannabis has not been legal to ingest.
Don't forget prohibition.
Immigration control is nonexistent.
Not one of the proposed new gun measures would have prevented any of the recent mass killings.
Every time a new law is enacted it requires both time and money. There is a limited supply of both, so the even "saves one child that argument" does not stand. Since there is a limit to both time and money using it inefficiently takes resources from positive and successful measures and wastes them on ineffective program. Basically creating two sets of victims.
Without exception the gun violence rates for cities in America with tight gun control are significantly higher than the ones that do not.
The highest penalties in American juris prudence is for murder. If that does not stop these evil actors why would lesser penalties deter?
Finally we are at least five minutes away if you can get to a phone or someone hears you scream, why should you not have the right to protect your life after someone else has decided to take it.
I understand the need and drive of people to seek instant solutions in the wake of tragedy but the real issue is not the object but the actor. Until we address the real issue of mental illness, nothing done to control objects will have any affect at all.