Well I did read it, but you addressed it by advocating the prison option, thereby risking murderers re-offending (and for the benefit of lynx4321, I'm talking psycho/mad dog murderers here - juries are for sorting out the various mitigating circumstances in individual instances), and paedophiles living another day to violate more children. My way ensures that will not/cannot happen.
So long as one properly funds and maintains one's prisons and allows for true life sentences, the risk is minimal. It is easily small enough to tip the cost/benefit ratio to imprisonment over execution. Beyond that, it is not acceptable to kill people on the basis of what they *might* do; which is what you're advocating. Doing so presents an incredibly slippery slope; leading us to some very dark and dangerous places as a society. Once you've decided that it's okay to kill someone because they *might* kill or rape someone, it's only a small step to apply that same reasoning to people who have never committed any crimes whatsoever, or whose crimes are trivially small. Why not kill the person who talks about having certain fantasies with his psychologist, even though he has never acted on them? Why not kill the alcoholic because he might one day get behind the wheel and end up killing someone? There's no end in sight. If you're willing to kill one person based on the possibility of them causing harm in the future, you should be willing to kill everyone on that basis.
Fortunately, legal systems in the developed world do not allow us to punish people for crimes they haven't actually committed yet and might never commit at all.