Man arrested for 2x4 labeled "High Powered Rifle"
The way I see it, weapons are tools, and different tools are appropriate for different jobs. Citizens have the right to shoot for sport or to defend themselves, and therefore the government should not be taking away the tools necessary for those jobs. But there are plenty of guns on the civilian market that are not necessary for those jobs, and there are plenty of measures the government could be taking to regulate guns that would not keep appropriate tools out of the hands of those who need them. The Clinton-era assault weapons ban, for instance, kept high-capacity guns and weapons with military-style accessories off the civilian market, but it didn't keep hunters from hunting or average gun owners from carrying a self-defense weapon around. And things like licensing and registration aren't a problem for anyone who isn't paranoid about needing to keep secrets from the government.
It is often the argument of gun enthusiasts that gun laws don't affect gun crime because criminals generally aren't using guns gotten off the legal civilian market. There's a lot of truth to this argument, but these kinds of massacres are a special case: they are almost always committed with weapons either legally acquired by the shooter or taken from legal owners by the shooter. This means that these kinds of massacres could very well be affected by gun laws.
On a side note, it's time for schools to change the way they design their buildings and procedures. Schools are built out of inflaofftopicble materials, they have sprinklers in every room, and their students and staff spend large chunks of time every semester practicing fire emergency procedures. And yet no student has died in a school fire in over 50 years. It's time every school had heavy metal doors that are kept locked whenever students are in the building and barred first-story windows, so that no intruder can just kick or shoot his way in, and procedures for dealing with an armed intruder that are practiced as often as their fire drills (Note that I am NOT advocating armed school staff--there's too much danger of students getting their hands on guns IMHO). These things could have saved a lot of lives at Sandy Hook.