I say it really depends on the situation. Some murders are justified. Killing a pedophile, Child molester, Rapist would be seen as justified for many people while killing a cheating man will be seen as gone too far. A lot of people feel justified when they kill someone who did many bad things before. In the end it is all about your concept of Morality that plays an important role to your opinion about this matter.
I think it depends on the context and circumstances of a situation. For example, If someone breaks into your home, Armed with a weapon, And is endangering your safety, You have a right to defend and protect yourself. Why would you let someone try to commit harm against you, And not make an effort to fight back in some way, Even if that means in an unfortunate circumstance, They end up getting killed. Also, Our body does flight or flight, With the robbery scenario, You don't have time to react to the situation, Or think about a plan, You're either going to hide, Or attack the person. On the other hand, If someone intentionally takes the life of another human being, Or premeditates their murder, That is unacceptable, Because they are well aware of the act they are committing, And they have a conscious moral awareness that what they are doing is wrong.
From a moral standpoint, There is no basis to hold one accountable for unintentional consequences. If someone comes at me with a knife and i push them away from me and that very knife happens to stab the person holding it in the chest and he/she dies, Then i had no knowledge that my pushing him/her would lead to that, Therefore, It is justified as it was not intended. Of course, There is a lot of room for legal disputes on this matter, I speak on the moral responsibility of such accidental scenarios.
If the person breaks in to the house and you need to protect your family it would be justifiable to use a gun and kill the person to save yourself and your family. Your family is the most important people in your life and if it is a choice between killing or being killed I would have to choose my family over the criminal.