I prefer to answer matters of controversy with facts and figures, since I find that they typically do a fine job of illustrating the point. Consider:
Of all countries in the world, around 50% have completely abolished the death penalty for all crimes; another nearly 25% have not had an execution in 10 years. This makes the US one of around 25% of the world's countries still practicing capital punishment.
Since 1973, over 100 persons have been exonerated from death row, some of whom had already been executed.
Almost all death row inmates were unable to afford their own attorneys.
According to California Commission for the Fair Administration of Justice, the current judicial system cost is $137 million per yer. If death penalty sentencing were abolished, it would be $11.5 million.
This was the info I provided to answer a similar question. It's up to the people who read it to decide how they feel about it.