Right to live
Everyone has an inalienable human right to life, even those who commit murder; sentencing a person to death and executing them violates that right.
This is very similar to the 'value of life' argument, but approached from the perspective of human rights.
The counter-argument is that a person can, by their actions, forfeit human rights, and that murderers forfeit their right to life.
Another example will make this clear - a person forfeits their right to life if they start a murderous attack and the only way the victim can save their own life is by killing the attacker.
No one has the right to take life from a person, and murderers violate this law, so you need to deprive these creatures of life.
That's true, no one has the authority to do that and that's not the best thing to apprehend criminals or something. Sometimes, it's better to give them a chance again but it's definitely not like the movies. You can get killed easily when the things are going rough, and if you forgave criminals, it might get you a bite in the back.
The dregs who committed the murder can not be given a second chance, because this will not help reduce the number of violent crimes. Evil must be destroyed.