I somewhat disagree that individuals do not have the right to kill another person in all cases, for qualified reasons of course. This begs two questions immediately. Do humans have the right to terminate their own life? And, are there logical or ethical exceptions to this ban on killing, personal or public?
I reserve any rights for myself not otherwise specified ethically or logically. By instinct, I will/can kill someone who immediately threatens my life, or perhaps even someone who threatens your life. Also, I favor the bombing of legal enemies during wartime, by reasoning that if someone innocent dies, that is the terrible waste of war, and good reason to avoid war. However, I am concerned over this last reason, because if I knew someone innocent might die, I would always reconsider. Therefore I never favor retaliation bombing of cities. Also, capital punishment clearly comes to mind here.
The logical flaw with capital punishment: If the argument is based on crime deterrent, then the IMPLICIT assumption is that anything that deters crime is also just, which is rarely the case using violence. Also, if capital punishment is based on punishment, then that is another issue which delves into the ethics of sadistic pleasure. If it is based on saving valuable resources to restrain a threat to society, then we have failed to demonstrate this, apparently, since the legal costs are currently more than incarceration, for good reason. Problems abound. But we digress.
Now, as per the assumption that killing another person is always wrong in all cases. Why? If you can untie that knot, then we can proceed. Also, we must avoid anthropomorphic fallacies, which tempt us to say that a fetus is the same as everyone else at all times (anthropomorphic fallacies are often based in monotheism, where one unknown God is always humanized, or dehumanized as the case may be). Also, the argument of human potential is also problematic. I can argue that someone in constant pain from an incurable disease can be permitted to self-terminate, or government-terminate (if comatose) for reasons of having no potential to gain from more expensive care that could be used for someone else. Thusly, we could likewise say that fetus has obvious potential, but considering it is an unwanted baby, healthy or otherwise, this argumentive potential is used against us at some point because there is more negative potential of costing society millions in medical bills or law enforcement.
Then there is the huge argument that we have been unjustly limited in this debate, that the true means of abortion prevention, like sex education and birth control, have been unjustly elimated, forcing us to debate the merits of unnecessary solutions. (To me, that seems to be the real problem here, we have been forced to debate abortion as birth control, which seems wrong because it probably is when considering that little effort has been publically to prevent it, and therefore little effort should be made publically to outlaw it, I could argue).
Now, why is it wrong to kill another person in all cases? It seems that this absolutist assumption leads to more suffering to me that cannot be easily justified, because if we say it corrupts our human sensibilities, that may be valid, but so does allowing civilization to stumble into dire poverty from bad breeding management.