I have been reading (on the advice of one of my correspondents) Robert W Brimelow's book, "What about Hitler".
The author attempts to answer the question that is a stumbling block for pacifists - is it right to stand by and let evil triumph?
Although I have not quite finished it, I can say that the author does present some cogent arguments about what constitutes a 'just war' and about the end not justifying the means, but so far I am not convinced by them. It may be OK to stand by and allow Hitler to march over you, but I still think that we have a duty to protect the weak from the strong.
Gandhi was asked towards the end of the war, "What about the Jews? Are you prepared to see them exterminated? If not, how do you propose to save them without reverting to war?"
Gandhi's response was that German Jews ought to commit collective suicide, which "would have aroused the world and the people of Germany to Hitler's violence." After the war he justified himself: the Jews had been killed anyway, and might as well have died significantly.
In the opinion of his contemporary, George Orwell, Gandhi did not understand the nature of totalitarian regimes and considered all struggles to be similar to his struggles with the British colonial government. While they might have encouraged Gandhi for fear of getting something worse - like car bombers or armed insurrection - they were essentially decent men with consciences. Not so the like of Heydrich, Himmler and Eichmann.
I also think that pacifist fail to realize that all order in society springs from the threat of violence. We may obey the law because we think it's right, but many obey the law for fear of getting caught. If caught they may be fined. Why pay the fine? For fear of imprisonment. Why submit to imprisonment? Because it is enforced by the threat of violence. In fact, even in states without the death penalty, resistance to the force of imprisonment is eventually met by lethal force. If you resist the arresting officer with firearms you are likely to be shot.
We may try to reduce the force used to control rebels against the authority of the state, but people have been killed by rubber bullets and by tasers, or even by being sat upon by three fat bobbies.
I will have more to say on this subject when I finish the book.