This is basically my position too, which is interesting given how far apart on the political spectrum @Its On A Slab and I are. If anything, I may be a little more absolutist than Slab is.As a rule, I am against it. But if someone does something heinous, and deliberate, and the evidence is clear (confession, DNA), I'm not going to lose any sleep over the outcome.
I don't see sufficient evidence that the death penalty deters many people. For example, those who commit the highest proportion of murders relative to their population - young black male gang members - expect (rationally) to live longer on death row if convicted than they might on the streets. As for others, given the relative frequency of mass shootings - from which the perpetrator rarely could have expected to escape unnoticed - again, it does not appear the penalty deters them. If one lacks the intrinsic whatever-it-is that prevents most of us from killing someone in cold blood, I'm not sure there is much any extrinsic penalty can do to compensate.
So if capital punishment isn't a deterrent, what purpose can it serve? Slab's adjectives - "something heinous and deliberate" - seem like the right ones, but what are they modifying? To me (and this is in keeping with mainline Christian apologetics on the topic), it should be something that indicates the perpetrator's complete rejection of our society's framework, such that irrevocably severing him from society is appropriate. Non-exhaustive examples would be premeditated murder of:
- Police officer.
- Active duty military.
- Elected officials or high-level appointees (e.g., cabinet members; supreme court justices).
- Masses in a public setting. E.g., the surviving Bondi Beach shooter; Dylan Roof; Timothy McVeigh.
- KSM? Not part of our society, so I'd keep him alive as an intelligence asset and day-laborer, letting God decide when to take him.
- I'm not sure how many people constitute a "mass."
- I say "in a public setting" because I would not apply it to a serial killer unless he met one of the other criteria.