I think the issue with the death penalty is not what it says about the bad guy. Its what it says about the rest of us!!! No one is debating that the criminals are total scumbags!  The question about the death penalty is why YOU think YOU can kill someone....with impunity! (I'm not impugning YOU personally!!)
I would also remind people that Pat Robertson, the ultra right wing "christian" preacher who runs the 700 Club stated that he believes we should have the death penalty for women who have an abortion!
The world is just plagued with psychopaths who like to portray themselves as "good" people!
And perhaps we should remember back to the middle ages  and even in the early days of America, when "Christians"  used to burn people at the stake......because they objected to witchcraft!