If those people hadn't been on death row, they'd still be rotting in prison.
If you give people the option of throwing someone in prison and forgetting about them, or forcing them to actually decide on their guilt, they will always choose the former.
If I was wrongly convicted, I would much, much, much rather be on death row than in for life-without-parole.
Fix the problems with wrongful conviction, lack of appeals, etc etc, and we can come back and abolish capital punishment.
But right now, it's naiive to advocate for abolishing capital punishment, because in the absence of other reforms, it simply makes the current system worse.
Halt capital punishment to prevent further, irreversible, errors. AND work on other reforms (better trial lawyers, more equitable appeals process, etc.). Then you can bring back capital punishment once we have a greater degree of confidence in the system.
Why do you think the rest of the first world has outlawed capital punishment?