Execution breeds violence in society
A State which supports the death penalty, in fact, states that killing is an acceptable way to solve social issues. If there is no man, there is no problem.
Society perceives this as an act of justice, and in consequence has a completely distorted concept of solving the problem of crime.
Citizens start thinking that the problems of crime can indeed be resolved by killing, and they do not think about the reasons that encourage or allow their fellow citizens to commit serious crimes.
The presence of the death penalty inevitably involves the society in the process of the issuance and execution of the sentence – people learn from the mass media (often involuntary) when a death sentence is executed, and this information eventually starts being perceived as natural.
“Let him be shot – why do we need to make fuss with him?”, that's the widespread opinion of common people when the state gives a legal force to cold-blooded, premeditated murder that is allegedly done for the benefit of society.
However, this primitive perception not only devalues the life of the culprit, but human life as such, showing that people can be killed.