I agree that it's negligible in the larger scheme of things. Even if the executions were done in an expedient (a la PRC) fashion, the deaths of a few innocents would affect few of us. But the significance to the individual on the receiving end of justice is great.
I consider that to be a rather negligible advantage considering how much time it takes to actually get through the execution.
I favor the rights of the individual over the cravings of the larger society. One might say the rights of the few outweigh the needs of the many. (Take that, Spock! Ya egg suck'n pinko commie!)