A Metaphorical Effort

OK let me try a quick metaphor:

People suffer from disease. Stem cell research may cure some of these diseases and thus alleviate suffering. Many embryos become human beings, but some of them do not. Therefore we should destroy many embryos to harvest stem cells.

People suffer from the financial burden of prisons. Doing away with prisons would alleviate some of the tax burden on upstanding citizens. Many prisoners are reformed and contribute to society as human beings, but some of them do not. Therefore we should exterminate prisoners to reduce the number of prisons.