The only mention of a right to life I find in the Bill of Rights is a stipulation that the taking of life be accompanied by due process of law. So the right to life must not be absolute.
It never was absolute.
Those who are guilty of capital crimes' lives have always been forfeit after a fair trial.
But the right to life of the innocent is absolute.
That's the key difference between a liberal and a conservative:
The liberal wants to protect the life of the guilty and allow the killing of the innocent.
A conservative wants justice for the guilty, and justice for the innocent.