What is the ruling on one who says that retribution for a killer by killing is a harsh punishment to deter people from killing, and what is the opinion on using the term "harsh"?

If the one who states, "Retribution is cruelty," intends that retribution is a severe punishment that prevents murder, then they have grasped the meaning correctly but erred in their wording. The more appropriate phrasing would be, "a deterrent and preventative punishment." However, if they intend that the ruling of retribution is unsuitable for civil life and contradicts human dignity, then this is blatant disbelief; for it is a detestation of what Allah has revealed. Allah the Almighty says: "But those who disbelieve, ruin awaits them, and He will render their deeds ineffective. That is because they detested what Allah revealed, so He rendered their deeds fruitless."