Why should the death penalty be Implemented in the US?
It should not. Human justice is by definition, human, which means it is subject to the frailties of humanity. Any legal penalties that have been passed can all be undone or rectified if an error in judgement is discovered, all but one. Wrongly executing a prisoner cannot be reversed. "A hundred guilty should go free rather than one innocent hanged." With the recent advances in DNA sequencing, suspected murderers have been cleared; death-row inmates have been pardoned. Enough DNA evidence has shown that there is evidence enough that the wrong individual could possibly be deprived of life, even when innocent.
Yet even if the evidence is iron-clad and a criminal convicted, the Death Penalty should not be implemented since that gives the power of life and death to the state.
The primary rationale for implementing the death penalty in a broad spectrum is due to the fact that individuals believe that the death penalty deters crime and makes a statement of society's intolerance for those who break the law. The compelling element of the death penalty is its overall statement about how individuals will be treated if they choose to break the law. The implementation of capital punishment would serve to ensure that others "think twice" about committing crimes. There is an equal amount of evidence and research present on both sides of the deterrence issue. I think that proponents of the death penalty point to these items as critical to their support of it.
You, yourself, asked this question a few months ago. Here is the link to the answers you got then.