I can't prove it, but I'm convinced that those who would avoid killing because they know there is a death sentence waiting (maybe), as opposed to life in prison, are so few as to be reasonably compared to my possible "deterent" as described above.
You can prove it.
Murders in the US are much more ( per 100000 inhabitants ) than murders in the vast majority ( all? ) of Western European countries ( per 100000 inhabitants ), where you have no death penalty.
That seems to prove the point that, death penalty, as deterrent, just does not work, quite the opposite, indeed.
Crime Statistics > Statistics > Murders (per capita) (Latest available) by country
Rank Countries Amount (top to bottom)
#1 Colombia: 0.617847 per 1,000 people
#2 South Africa: 0.496008 per 1,000 people
#3 Jamaica: 0.324196 per 1,000 people
#4 Venezuela: 0.316138 per 1,000 people
#5 Russia: 0.201534 per 1,000 people
#6 Mexico: 0.130213 per 1,000 people
#7 Estonia: 0.107277 per 1,000 people
#8 Latvia: 0.10393 per 1,000 people
#9 Lithuania: 0.102863 per 1,000 people
#10 Belarus: 0.0983495 per 1,000 people
#11 Ukraine: 0.094006 per 1,000 people
#12 Papua New Guinea: 0.0838593 per 1,000 people
#13 Kyrgyzstan: 0.0802565 per 1,000 people
#14 Thailand: 0.0800798 per 1,000 people
#15 Moldova: 0.0781145 per 1,000 people
#16 Zimbabwe: 0.0749938 per 1,000 people
#17 Seychelles: 0.0739025 per 1,000 people
#18 Zambia: 0.070769 per 1,000 people
#19 Costa Rica: 0.061006 per 1,000 people
#20 Poland: 0.0562789 per 1,000 people
#21 Georgia: 0.0511011 per 1,000 people
#22 Uruguay: 0.045082 per 1,000 people
#23 Bulgaria: 0.0445638 per 1,000 people
#24 United States: 0.042802 per 1,000 people
BTW.
I have canceled my trip to Colombia..
If that is the case the only choice remaining is whether "we" want to kill because it makes us feel better, or not kill because that makes us feel better.
Basically, I have the opinion that pro-death penalty people are driven, in their opinion, by a false feeling of gratification.
He took a life, but, thanks God, his life was taken too.
Which makes us not so much nobler than the killer.
Disclaimer
What stated above is just my own personal opinion, and I may be wrong.