If one believes the corporate CEO is personally responsible for the deaths of hundreds or thousands of people, there are quite a few measures that can be taken short of murder.
I don't condone the murder of the abortion doctor regardless of what the murderer believed, but he, obviously, didn't require my affirmation. Because he felt the murder was either equitable or ultimately life-saving doesn't change my opinion that he was both wrong and bent.
Your original question, it seems to me, must be answered in the context of commonly accepted mores. As a society, we have adopted a certain framework in which to co-exist. Because someone believes actions outside of that framework are justified only makes them so in their individual regard. If that actually represents justification then all we need to judge is the sincerity of every madman and monster.
If morality has any practical meaning it can't be predicated on the personal beliefs of each and every individual on earth.
Your moral obligation in confronting an unjust system is to heroically challenge it through methods that ultimately conform to the moral framework of the world in which you live.
For most of us (certainly as respects Americans) this does not preclude violence, but it does preclude vigilantisim.
It really isn't tough to identify the right action to take, but it can be very tough to take that action. We are far more threatened by the selfishness and cowardice of our fellow inhabitants of the framework, then we are by the kooks who live and rationalize outside.
Such kooks are, clearly, able to effect dramatic instances, and some that could have far lasting implications (What if Obama really is the Messiah and some nut assassinates him?), but their actions are always recognized as falling outside the framework and are as predictable, preventable and regrettable as a random natural event.
Bottom line: No one, who does something the rest of agree is freaking crazy has met their moral obligation.