Honestly this is BS that stems from a belief that even if you know for certain that a person is guilty of murder that they should not be put to death.
There are acceptable margins of error for everything. To claim that the death penalty is "special" and should be held to some impossible standard just means you oppose the death penalty in general.
As an obvious example for why your standard is full of it consider this: http://forums.anandtech.com/showthread.php?t=2301811
Apparently even something as simply as ibuprofen has something like 1 in 100,000 people have a severe adverse reaction to it. If we applied the same standard you wish to apply to the death penalty to ibuprofen it should be banned from sale. While in reality you can walk into any Walmart and buy it no questions asked.
Uhh, yeah, killing someone because you believe they committed a crime that they didn't is KIND OF SPECIAL. I knowingly accept the risks of taking Ibuprofen when I take it. Are you suggesting I should accept the risk of being wrongly executed for murder every time I step out my front door? That is some of the most dumb ass logic I've ever seen.
Why don't you answer the question I posed? Are you willing to be that "margin of error" guy that gets wrongly executed? It's OK I guess so long as it's someone else, right?