In the thread linked above, an anonymous commenter argued that those who oppose abortion should not support capital punishment. For those who aren't aware, I oppose both the death penalty and abortion, but I don't think his logic works.
Abortion, I think it's clear to all but the most die-hard partisans who take the time to think about it, is the taking of a human life. Not one that's completely developed, but a life nonetheless. The death penlty is as well. However, the death penalty, when appropriately applied (ignoring for the purposes of this discussion executions of the innocent which hasn't been proven in this country), is the taking of a person guilty of some crime, usually most heinous. By comparison, the victim of abortion's only "crime" is existing as the result of some action of his or her parents.
That's the fundamental difference between abortion and the death penalty: innocence. If you believe capital puinishment to be wrong because it takes the life of a violent criminal, how can you support an action that takes the life of an innocent without any sort of legal process at all?