There is a big difference as to whether or not an individual deserves to die and to whether or not implementing capital punishment is a good idea.
I believe that there are some henious murderers such as the likes of Harold Shipman, Nikolas Cruz, Dylann Roof, Ted Bundy, and the Wests that absolutely do deserve to die, but in reality implementing the death penalty against them was/is/would be a very bad idea for four reasons:
1. It's costly - it costs around four times as much to conduct a death penalty case than to conduct a life imprisonment case. I'm not sure about you, but I'd be fine with substituting the death penalty with life imprisonment even when the defendant deserves it if the money that would be spent on pursuing the death penalty can be spent better elsewhere.
2. It means that we can kill innocent people - in my view, executing people who deserve death is not worth the potential cost killing innocent people.
3. It cannot be properly executed humanely.
4. It carries an unacceptable racial bias when properly applied, and we have time and time again seen especially in the US people (typically white) getting life sentences for crimes as severe as murdering their entire family due to arrangements such as plea bargains and others (typically black) getting the death penalty for far less henious murders.
