"But that wouldn't have stoppped THIS incident"
There are a number of arguments of the form:
Proposal X is ineffective because it would not have impacted the Sandy Hook massacre.
Arguments of this form fail to recognize what is "the problem", and how "the problem" may or may not be impacted by Proposal X.
People making arguments of that form fail to realize that "the problem" is not THIS incident. There is a larger and broader problem which has been brought to a head by the visceral impact of this incident.
Yes, every situation is different, and may be affected by an infinitude of factors. Against the daily - daily - carnage of misuse of firearms, the Sandy Hook incident is "off the charts"; waaaay out in the skinny end of the run-of-the-mill small horrors we have tolerated too long.
The thing is, the way you shift the skinny end of the curve is to shift the entire curve.
Quite obviously, this incident would have been totally preventable by having a law stating, "No person shall have a son named Adam Lanza and live in Newtown, Connecticut". That law would have impacted virtually NOBODY in the general population, and would have completely prevented this from occurring.
But "preventing THIS from occurring" is not the goal. This incident is the straw which broke the camel's back on the mundane casual gun violence we experience each and every fucking day.
So, may we please dispense with the analysis of "whether or not Proposal X would have had an impact on Sandy Hook"?