Response to Sam's Question

Q:  Do you believe that it is within human rights to sentence criminals to the death penalty?

My colleague Sam is asking a question that ethicists, politicians, and theologians have been asking for centuries. I think that humankind has a basic right to survival, since survival continues the human race. Therefore, things that decrease mankinds chances of survival would be considered undesirable. Self defense is a way to preserve one's self, no one can argue with that.Therefore, defending oneself from someone who would wishes to harm someone would be considered an act of survival. 

Now, in my view, a human life is priceless, and anyone who takes another life commits a heinous crime, yet they might be able to be redeemed and focus their future on a better path. However, if a person has taken human life and shows no hope of redemption and threatens the life of future persons, society as a whole is allowed to sentence that man to death which will protect the survival of their race

Who gets to decide who is irredeemable?