Killing someone off of some list is murder. Period. Total chaos if this became the norm. You would have people killing people for walking on the grass in the end. Is that what you want? Total anarchy?
And if you don't think that would happen, take a good look at NO.
We're already there. Have you seen how many sexual predators are out on the streets?
It is a little crazy to compare killing a child rapist to killing someone that walks on your grass.