It is the duty of society to protect ALL of its citizens.
Even those who, by their actions, have placed themselves
outside the law. Whether or not you believe in the death
penalty, it is fairly well agreed upon that the only entity
that has a right to kill with due deliberation is the state.

Vigilante justice devolves into mob rule. Its a
restatement of the principle that power corrupts, absolute
power corrupts absolutely.