There are two very good reasons to execute criminals.
1- There is zero possibility of repeat offenders.
If you are so worried about repeat offenders, then why do you limit death penalty only to murderers? By your logic, we must execute all the criminals, whether charged with murder or stealing a loaf of bread. That is the only way to ensure that there are no repeat offenders.
If you release a convicted rapist, robber, swindler etc. after he has served his sentence, there is always the possibility that he will offend again. So why restrict death penalty only to murderers, why not apply it to all the criminals?
The argument doesn’t make sense.
2- Taxpayers do not have to support them.
The real problem is our soft on crime liberal joke of a justice system that gives criminals more rights than victims.
But taxpayers do have to support them. It is much more expensive to execute a murderer than to give him life without parole, as is the experience of USA.