"An Extreme Luxury Item"

If not on moral grounds or to eliminate the application of unequal justice, perhaps a monetary argument can put the final nail in the coffin (excuse the pun).

From Reason...

The popular impulse to put people to death is just not what it used to be.

Executions have fallen by half since 1999. The number of new death sentences is about one-third what it was at the 1996 peak. Even in Texas, long the leading practitioner, death sentences are off by 80 percent. Several states that retain capital punishment have not administered a single lethal injection in the past five years.

The exoneration of 138 death row inmates has weakened public support for the ultimate sanction.

Franklin Zimring, a law professor at the University of California at Berkeley, says capital punishment has become "an extreme luxury item." Maryland has spent $186 million on capital cases over the past 30 years—which comes to $37 million per execution. A 2005 study pointed out that "New Jersey taxpayers over the last 23 years have paid more than a quarter billion dollars on a capital punishment system that has executed no one."