I am unclear on how this story is contrived. There are vast numbers of business with terrible externalities today; this is deeply related to the debate on climate change. Alternately, we have large cutting machines and those machines don't care whether they are cutting trees or people; if a wood chipper could pick things up but not distinguish between which things it was picking up it would be very dangerous (but still very useful if you have a large space of things you want chipped).