This question is debated on here regularly and the same arguments come up over and again. Those who think it is acceptable will never change.
Just a couple of points, 10 Clarion St, the death penalty has been abolished permanently for ALL offences , treason was still a possible death penalty offence until after it was abolished for murder. But the death penalty no longer exists for any offence. It was finally abolished in 1998
https://en.wikipedia.org/wiki/Murder_(Abolition_of_Death_Penalty)_Act_1965
Ian Brady has been mentioned, Brady was pleading for decades to be allowed to commit suicide by starving himself to death. But it was not allowed ,he was forcibly tube fed for over 10 years to ensure he really did stay in prison until the end of his natural life as the sentence demanded.
naomi, mentioned public safety as a reason for killing murderers , well locking them up until the end of their natural life as is done for anyone who gets a 'whole life tariff' will do that.
Repeat and multiple murderers are among those who can receive a whole life tariff so that is another argument settled.
I think nalit and I are the only ones on AB who have actually met and talked to murderers , all the ones I have met are just normal people who had a one off moment of rage or lost control during an argument or after abuse. A death penalty would have done nothing to stop them.