The discussion seems to be turning towards what should be done now which is a very good thing IMHO. If we are to weather this storm without substantial blows to our rights, we're going to have to be able to offer meaningful and easily articulable solutions of our own rather than just rejecting any and all new proposals.
I think that most of us can agree that a new AWB or similar gun control laws are not the answer here. Lanza undoubtedly broke numerous state and federal gun laws in the commission of his heinous actions and it seems obvious at this point that he neither respected the law nor feared the punishment for breaking it. Because Lanza had no regard for the law and because there is no reasonable way to make every possible means of committing mass murder unavailable, it seems to me that focusing on the tools Lanza used is the wrong approach.
Mention has been made of Lanza's access to his mother's guns. I think it's really too early to make judgement calls based on that because we still do not know exactly how easy it was for Lanza to gain access to said gun. More broadly, I think that mandating all gun owners to keep their firearms locked away from children is a more complex issue than many might think and is frought with unintended concequences. Not all children are the same and some are psychologically and emotionally stable and mature enough to be trusted with firearms at a remarkably young age while others obviously are not. Compounding this, children can, have, and do use firearms for lawful self-defense more often than one might think. While not a perfect solution, I still feel that the ultimate decision about how much access a given child should have to firearms should remain with that child's parents or legal guardians. I would have no problem holding adults legally responsible for crimes or negligent accidents that minor children might commit with their firearms, but such is already the case in many, if not most, jurisdictions. Lanza's case is somewhat different, however, in that he was 20 years old and thus legally an adult himself.
The mental health issue is another in which we should tread carefully. Mental health is one of the most complex areas of medicine and there is surprisingly little consensus on the best treatment and even definitions for many disorders. While the litmus test for abridgment of rights is generally whether or not individuals poses a danger to themselves or others, that is not as clear cut as we'd like it to be. We must be very careful that, in our attempts to keep guns out of the hands of the extremely small number of people who are dangerously ill that we don't abridge the rights of those who are not unnecessarily. The more important facet of mental health that I think needs to be addressed is the availability and quality of mental health care in our current system.
The final, and IMHO most important, issue that needs to be addressed is the security of our schools. No matter how restrictive our laws nor how good our mental health care system, someone will eventually slip through the cracks and attempt to do something horrible again. We need to transform our schools from "soft targets" into "hard targets" where people like Lanza are not free to carry out their deranged intentions while meeting little or no resistance. It is no accident that these sorts of mass murders usually occur in areas with little or no police presence and where the victims are likely, if not guaranteed, to be unarmed.
Some have proposed stationing armed guards in schools. As Tom Servo has pointed out that presents financial problems particularly for small communities without deep coffers. These financial problems could, I think, be addressed through the allotment of federal funds to districts that cannot afford such measures on their own. Furthermore, this whole "gun free school" nonsense most certainly needs to be re-examined. Lunatics like Lanza obviously do not care whether or not guns are banned on school property while the ban serves to ensure that the victims are helpless. I see no good reason that school faculty, and in the case of colleges students, who meet the legal requirements to carry a handgun for self-defense in their state should not be allowed to do so in a school. The whole property rights argument of schools (colleges in particular) has lost me, your property rights do not trump my right to self-defense.
I contend that reference to the start of this grand experiment is relevant though.