I have to give you that one, Thorne. I'm guilty of blurring the distinction between corporal and capital punishment.
No-one executed for murder has killed again afterwards: even the ones who were innocent and, it might be argued, had a "free strike". A crude but highly effective means of punishment. Maybe that's why our forefathers used the death penalty on highway robbers, adulterers and sheep stealers too. One shouldn't disregard the wisdom of the ages lightly.
Knives are becoming a problem at our schools, and a few of them have installed metal detectors at all entrances. Maybe that would work in USA universities. But, thinking about it a little more, if I were intent on carrying out a mass killing, I wouldn't let anyone stop me at a metal detector - I'd run past then open up, probably taking out the guard as my first victim.
TYWD