Just to play the Devil's advocate, aren't you in fact presumptious to consider you have the insight to act correctly, and are making a false dichotomy between action and inaction in the case you cite? As John Milton says in his poem 'On His Blindness', 'they also serve who only stand and wait'. The Universe does not need us for good or bad. You say you are not blaming the hypothetical inactor, but your write-up is shot through with the assumption that they have failed in a moral sense.

The Dao De Jing says the Way lies in 'wu wei er wu bu wei' doing nothing there is nothing that is not done.

Perhaps you stand up for your rights, resisting the Nazi invaders in wartime Yugoslavia and they shoot twenty villagers for every Stormtrooper the Partisans off. Were you right or wrong?

That all said, I agree with Kenzilla. It's a knotty philosophical problem, but in most real life situations you gotta do what you gotta do, and liberation is down to us. I just like to remind myself from time to time of the Ultimate Emptiness behind my choices.