You mean besides the fact that capital punishment, properly applied, serves as a deterent on two levels?
First level is that there's no record of anyone punished so permanently has ever turned recidivist.
Second level is that when capital punishment is applied as the natural outcome of heinous crime, without the media circus, the little whiny left-winger hand wringers crying outside the prison, without the all the petty absurd emotion that goes with the bed wetters upset that a killer is being discarded, when, in fact, the punishment is applied routinely and surely, and most importantly, SWIFTLY for certain acts, people stop and think before they commit those acts themselves.
There's something wrong with someone who can shed a tear for a Jeffrey Dahmer, a Jose Avila, a Charles Manson, to name a few .