It shouldn't exist.
And I really don't believe this should require justification.
Allow me to break it down:
– The action of intentionally taking the life of another is homicide
– The action of unintentionally taking the life of another is manslaughter
– Murderers generally believe themselves to be above the law, thus their actions
– The death sentence is the action of taking the life of a human being
So, how is it any different? Why is the law system allowed to commit actions that the general people aren't?
Point stands, case closed, next.