I believe killing without reason is wrong and not justifiable at all but things like war, euthanasia and abortion. In war, you are killing an armed combatant and I do not believe that is wrong but to purposely kill an unarmed, non-combatant person is murder. I don’t think war is wrong because it is most of the time necessary. For example, a few years Iranian president Mahmoud Ahmadinejad vowed to wipe Israel of the map and the only thin Israelis could do was to defend their country from the Iranians through war. On the other hand, war is sometimes unnecessary, for example, jihadists declaring war on non-believers.
In the case of euthanasia, I think it is right because I think helping a person to end their suffering is sometimes the most loving thing a person can do for them and also people have free will and have the ability to think for themselves and so should be allowed to choose. Situation Ethics is easy to apply here; you can dispense with rules about killing because the most loving thing to do may well be to give someone a peaceful death. Situation Ethics is personal - it puts people before rules. It is also pragmatic, allowing us to do whatever works best in the circumstances. What is the use in keeping someone alive to suffer? Relativism is at the heart of the theory. This means that in any situation, when faced with a difficult decision about whether to help someone to die, we need to act out of love, which means ignoring any hard and fast rule and doing what the situation requires. On the other hand, Kant’s theory disagrees with this, for Kant, the outcome of an action is not relevant to whether or not it is ethical. This can easily be demonstrated - sometimes evil actions lead to unintended good consequences. He also disagreed with making moral choices out of compassion, kindness etc. When considering euthanasia, then, Kant will not be interested in the level of suffering of the patient or relatives. He would not agree that we should do the loving thing. He would work out what the right thing to do was.
As for abortion, I think it is the right thing to do because a woman should be allowed to decide what to do with her body. I agree with utilitarianism which is generally pro-choice. Utilitarianism is teleological, concerned with ends or outcomes. Utilitarians would ask whether having an abortion brings about the greatest good. Having an abortion because of financial pressures, other family members' needs, education, work are justifiable reasons. It may in some circumstances be right to deny a woman the right to choose to have an abortion if doing so would bring about the greatest good.
An example of a current affair which questions whether killing is morally justifiable is the when UK forces shot British ISIS fighters in Syria. This is killing but I think it can be justified because if the UK forces hadn’t shot the ISIS fighters then they would have tortured and killed innocent people. Another example is one where 2 white-American police officers shot a black teenager because they suspected he was in possession of cocaine. I don’t think that this is morally justifiable because they had no reason to kill him. First of all possession of cocaine isn’t a good enough reason to murder someone and secondly he was only a suspect, they shot him even though they were not 100% sure that he was in possession of cocaine.
In conclusion, I do think killing can be morally justifiable depending on the circumstance for example for self-defence.