... seem to have forgotten about that study in the nineties that applied the then recently developed DNA sequencing techniques to old cases. Said study proved conclusively that about a 20% of the executed were innocent. It can be logically inferred that nowadays the % of false convictions is close to that, excluding (most) cases where DNA evidence is used.
And the problem with the appeals is that every official involved in the case has an interest, a set of perverse incentives, in upholding the death sentences. No policeman, attorney or judge wants the public to know that they helped to sentence an innocent to death. The result: the appeals process is an uphill battle against the establishment, and most people lack the resources (money) to carry out a successful appeal.
Other studies prove that witnesses are far less reliable than generally assumed, that often the cops and district attorneys put too much pressure on witnesses and suspects, or directly manipulate or hide evidence that could set the suspect free.
Is the American legal system perfect and free of errors and corruption? Can you resurrect a wrongly executed person? If you can't answer affirmatively to at least one of these questions, death penalty is just another crime.
To further clarify my point, most of the convicts in the death row probably deserve to be executed, but the rest of the population doesn't deserve to live in a country that has that kind of power over its citizens, because that power will be -and has been- abused.
Let the downvotes begin... . Anyway this needed to be said.