It justifies nothing, but it does make it an expected response... there is a huge difference between these two you two seem to be missing.
The world is unfair, when a cop pulls me over I kiss his ass because while morally I should be able to say "fuck you" in practice I expect that will make my life harder. Sure the cop is in the wrong, but doesnt change the fact im spending the night in jail. When i make my choices I must do so being aware of what is likely to happen, not what is justified in happening.
Same here. you murder a population you should **expect** them to try to murder you. It is wrong, and in an ideal world they wont. But in all reality we know how the world works and we know they will.