Retail solutions for problems in education, for example, include firing inept teachers, returns to basics, tougher discipline, vouchers, etc. Support for these is limited almost exclusively to conservatives.
Wholesale solutions to education problems involve spending more money, or making changes to society so that there aren't any more poor people, etc.
In crime a retail solution is harsher and more certain punishment, while a wholesale solution is "removing the root causes."
One constant in the comparison between retail and wholesale is that the wholesale solution, if it is indeed such, require many years or even decades to have any effect, while retail "solution" can be implemented quickly.
Your "solution" is really not one of preventing such attacks. If an armed and trained shooter had been onsite in CT, he would probably not have prevented the attack, although he might have been able to limit it. Had the shooter known an armed person was onsite, he might have launched the attack anyway, or he might have diverted to a site where armed response was less likely. For example, what is to stop an armed man from shooting his way onto a school bus at a stop?
IOW, armed response does not prevent surprise attacks at all, although it can hopefully limit their severity and reduce the number of victims.
Liberals, in general, think there such attacks should be "stopped," that the chance of their occurring should be eliminated. The only way to do this is to change society by making it impossible for a nut to get his hands on a gun.
Even if such changes could be made quickly to laws, any effect is going to be very slow, requiring many years or decades to reduce the huge numbers of guns.
But liberals don't really care about that, as they are more interested in making the changes than in whether they are truly effective at working towards the stated goals.
NOTHING will stop crazy people from being crazy, and that is the point I attempted to make. What would “stop” a person hell-bent on perpetrating an atrocity such as this with a claw-hammer? A well armed and trained citizen.
The same (and only) thing that will stop the atrocity being committed with any other weapon, guns included.
An unarmed middle-aged (or average female) teacher will not withstand a dedicated and sustained hammer attack by a motivated 20 something male, any better than they will withstand gunfire if they are not trained and equipped to defend themselves. The police, just like in the recent shooting, will arrive after far too many lives have been destroyed.
My point is this: No proposal offered so far will allow those charged with protecting these young lives while they are outside their parents care to be successful in doing so.
The only solution that I can see to mass murders of any type, in any location, will be tightly controlled return-fire by someone who is actually on the scene at the time the attack is taking place.
Again, I posit that you CANNOT stop crazy people from being crazy.