Loughner was not responsible for the magnitude of this tragedy. We should not blame him for that magnitude any more than we would blame a wild animal. In a free society, we must expect lunatics like this and prepare for them.
You want to blame me for the carnage? Okay, I accept. I'm to blame because I stopped carrying when Sheriff Hutchens took away our permits. Plus since then, I don't dry practice enough. When I did carry, I once had to present my weapon in self-defense. Because of my training, once the threat materialized it took me only one second to get my weapon out to the low ready (I measured the time on a recording of the incident).
How many people can die in one second? How many people can be saved after that first second? I guarantee this tragedy was barely unfolding at that point and MUCH could have been done to stop it.
Worried about shooting in a crowd? First of all, a supermarket is not so confined that a "crowd" would exist for this long with gunfire. Whatever crowd existed would disperse pretty quick. And if there was, so what? Someone could have gotten close to the shooter and knelt or fallen to the ground where a head shot could be made at a safe angle in that critical second. We know that one hero did run to the fire to help people.
Who to blame? I blame everyone there that chose not to defend themselves. Except that poor little girl. Evil triumphs when good men walk out the door without a sidearm enabling them to "do something" if necessary.