Is it justified to perform a small evil to cause a greater good? Would you take one life to save ten? But who are you to take the life of anyone anyway? In real life you don't have perfect knowledge of any situation and, hence, cannot operate on such extreme as we do in examples . You know nothing of the one life you'll take or the ten you will save, and you would not know of what they might have contributed to the world, positive or negative. Would you tell a lie, steal, cheat, or be dishonest to yourself, all because it is means to find yourself in a position of tomorrow where you can cause the greater good for everyone?
An example would be a Robin Hood scenario where you are committing evil by robbing, but by evil robbing and giving to the poor you are actually doing right by doing wrong. As with any of this example though, it really comes down to the level of comfort you have in your decision and your personal morals. So maybe it is not a right vs wrong on scale, but how much wrong a person is comfortable which would define their choice?
In another case maybe I could agree with small evil vs big good, but how in the case of taking life? Life is never small in my opinion, so the scale does not translate like that.
But … suppose a man is attacking me personally with a weapon that could cause death or permanent serious injury. Killing him is an evil. But by attacking me he devalues his life in comparison to mine enough to justify choosing his death over my death, or even over likely serious injury to me. This is clear to me, although I know not to all. But to go on. Now suppose I'm not the one being attacked, but it is my child or my wife. Now suppose it wasn't a family member, but a neighbor. Now suppose it wasn't a neighbor, and the attack is happening in another country between people I don't know and whose language and culture I don't know. Along this spectrum, when if ever do I step out, and say, I shouldn't take the attackers life if I have the means to?
When it comes to "fight or no fight" type of scenario, the question is pointless, instinctual behavior will take over. Karma, which has no mind, should decide death. Not people.