You can't predict the future.
Why punish the child because of the crime of the father?
Also, scientists agree that life begins at conception, also referred to as fertilization. Drs. Keith Moore and T. Persaud’s embryology textbook used by medical students at the University of British Columbia confirms this:
Human development begins at fertilization [emphasis in original], the process during which a male gamete or sperm (spermatozoon) unites with a female gamete or oocyte (ovum) to form a single cell, the zygote. This highly specialized, totipotent cell is the beginning of embryonic development. The zygote, just visible to the unaided eye as a tiny speck, contains chromosomes and genes (units of genetic information) that are derived from the mother and father. The unicellular organism, or zygote, divides many times and becomes progressively transformed into a multicellular human being through cell division, migration, growth, and differentiation.
What about the holocaust. If it didn't affect us personally, should we have just stood by and let it happen?
Whether I agree or disagree, that is so? How does that convince me in the slightest?
If you went into a coma, there's no telling when you would recover. You wouldn't be able to live independently, but that doesn't make them parasites. Also, patients can have a temporarily flat EEG, but shortly after, have a functioning brain again. In that time frame, would that person be not human? Would we be allowed to kill them?