There's the liberal idiocy of the FQ we (sort of ) missed !
Capital punishment may not be perfect but over the last 6,000 years it has worked considerably better than anything else that has been tried.
As to the imperfections of the system, the number of people being released due to DNA evidence is not a condemnation of the system at all, but in fact proves that reasonable successful efforts are made to minimize the number of innocents wrongly convicted.
Considering the average time on death row the anti DP argument ignores the fact that Capital punishment is simply one punishment, it is no better to put an innocent person in prison in the first place than it is to inflict any other punishment on him.