There are several reasons one could argue in opposition to the death penalty as a legal consequence for convicted criminals.
Convicts who are sentenced to death are granted an extensive appeals process, which means they usually stay on “death row” for many years before facing execution. Part of this appeals process includes exorbitant court costs that are subsidized by the taxpayers.
Another reason is that there is always a chance someone innocent is convicted of a crime he or she did not commit. It would be a moral travesty if an innocent person were killed.
Lastly, capital punishment is somewhat hypocritical. If we as a society condemn murder, then we should not then murder the murderers. This represents an ideological paradox, and it goes against our pledge to eliminate “cruel and unusual punishment.”
So, you could include these reasons in sentence form. I have included a sentence stem below for your convenience:
Because of ______________, _______________, and ______________, the death penalty should not ___________________.