Don't forget to take away cars and anything that could lead to a fall. Those both kill more people a year then guns. And we should outlaw suicide, it kills 3 times as many people as guns do. Heck, you're more likely to die by accidental poisoning then you are by a gun.
As for his odds of killing 32 with a knife, that would be hard to do. But how hard would it be to kill 32 with a fertilizer bomb? (168 dead, over 800 injured in the Oklahoma City bombing) Still, it's easier to say that if we just got rid of guns, then we'd all be safer. After all, no one was ever killed by another human being before we had guns.