In every option Sixty mentioned murder is justifiable, and even more cases. Murder is justifiable to bring about social change.
For example, let's look at the civil rights movement. Americans have been taught to think that blacks were slaves, and then Martin Luther King Jr. gave a flowery 'dream' speech, and then everybody loved each other. In actuality, 'I have a dream' didn't actually do anything but be a source of good sound bytes. Blacks had been protesting peacefully for equal rights for many, many years. Not only did people flat out ignore them, they kept killing them, raping them, exploiting them, and teaching their children to hate themselves. "Aw lookit dem cute little niggers out in the street, wanting 'equal rights'. Just ignore 'em, they'll go away." What got black people equal rights was not peaceful little marches, it was a large portion of the black community that had gotten fed up with their goverment ignoring them and popular culture shitting on them at every turn. They basically said "You want to ignore our peaceful protests? Fine. How about every time you kill one of us, we kill one of you? Every time you rape one of us, we kill one of you?" And they did it.
It was THIS that got blacks their equal rights, not some fluffy bullshit. It took the black community going militant and SCARING THE SHIT out of the upper class whites that got them their equal rights. And of course, this very movement has now been largely demonized in our own current culture - they were called the Black Panthers.
Real social change only happens if people die, and those groups wanting real social change need to realize that anything they do that's short of it is pretty much meaningless. When a social group is SO marginalized that every movement they make is viewed as negative, and their very existence is seen as disgusting - murder is a very justifiable tactic, because it's all they have left.
As for other instances where murder is justifiable - Our entire culture is built on us standing on the backs of third world nations. It's how we're so wealthy. When they get wealthier, we get poorer, so it's actually in our best interest to keep exploiting and killing people in other countries because it's how we can live so nicely.