It is bad for humanity to play the role of executioner. It hardens us to taking life, which overflows into social interactions on the streets, raising the crime rate and the chance murder will take place. It also leaves no room for the mistakes we fallible humans make, and make regularly. How many convictions for murder have been overturned when DNA evidence proves somebody convicted of murder didn't commit the crime? If we kill one innocent person, we have killed far too many due to failures of our criminal justice system. Living in a country far from free of the ills of racism, misogyny, and many other social ills, we are not the greatest judge of who is worthy of death, especially among minority populations.
Keep people who have committed horrendous crimes off the streets, yes. Put them away for life if need be (all though restorative justice would be far better for us all when possible). But stop harming us all by state sanctioned executions. We all will be better off for that.