I disagree that the deterrence would be significant enough to justify the death penalty. But I don’t think our disagreement matters. Even assuming what you say is true, it’s not worth the lives of the innocent people who will be found guilty and executed, in my opinion. I also think it’s a bad idea to give the government the power to kill its own citizens. So even if you are correct, I have other objections that outweigh the potential deterrence factor.