Justice is a matter of ambiguity. Everyone has their own set of moral guidelines, and the idea of 'justice', is, ultimately, the manifestation of these guidelines projected onto a situation regarding legality. However, the economic and social benefits of capital punishment far outweigh, in my eyes, any objections to the practice of capital punishment centred around "but killing is wrong! :(((". Criminals who have committed crimes warranting their termination by the state deserve nothing more than it's swift implementation. Play stupid games, win stupid prizes.
I believe criminals should not be executed because being imprisoned for your entire life is much more torturous than being killed right off the bat. Also there's always the chance of someone being framed. Can you imagine if a completely innocent person get murdered from a crime he/she did not commit? And finally, what if the murderer has a severe mental illness? Although it is still inexcusable, they could go to a mental institution or prison, instead of being executed for a condition they cannot help having.
Some criminals kill because greed and most of the times they lose conscience and do it multiple times. Today on the news, a 4 year old child got stabbed 24 times for what reason? Greed. So id like to see criminals not just die but to be punished. Something like inhumane style of suffering. Hahahaha