That statement assumes that the 'crazy man' used his fingers to shoot the children because the gun didn't make any difference at all to them!
That comment is the most crass made by people in denial, because, compared to all the other category of weapons, guns are in a class of their own. They are lethal killers because you do not have to be near a victim to shoot them dead, as you would need to do with a knife, hammer, strangulation or other weapon. With guns, you can be as detached, merciless and callous as you wish when you face a victim.
A crazy man used GUNS to kill those children. If he had used a knife he would have taken longer and some of them might have been spared. One can even wrestle with a knife to save one's life, but one cannot wrestle with a gun. Guns are favoured by killers because of their cold killing power, especially from a distance. Until killers can point their fingers at people and kill them with those fingers, one cannot separate a gunman from his weapon. It takes BOTH to cause the terrible damage.
Choosing a gun was not an accident for Adam Lanza. It was a deliberate decision because it cold cause maximum damage in the minimum of time, and that's the point gun lovers are deliberately ignoring. Furthermore, no one is blaming everyone with a gun. Most people are worried about the accessibility of guns, the way guns are promoted as some kind of crucial harmless accessory and their availability to crazed people wanting to create havoc - the very issues that gun defenders are not addressing. But the sheer number of people killed with guns in America compared to other countries suggests that something is terribly wrong with the gun culture that needs to be addressed.
In the end, the man is as important as the weapon when it comes to firearms because they are in a class of their own. Man or machine, it will not make any difference when the next crazed gunman points that firearm at vulnerable people and exercise his power in snuffing out their lives.
So one can justify guns as much as one likes, but it is all about priorities: Which is more important, guns or your children?