I think a good point would be to view it in terms of laymen and monks and nuns
Monks and nuns have made a dedication to the precepts and to nibbana, with a renouncement of wordly life, for them, killing wouldn't be an option
However laymen, while accepting the Buddha, have only taken the basic precepts and are very much a part of wordly life and being a part of worldly life would mean taking worldly action, in extreme situation, such as in the case of the Third Reich
I can think of a good thought experiment which is quite widely used in ethical philosophy - If you had a time machine, would you go back and kill Hitler as a baby, or as a teenager or at any point before he joined the German Workers' Party?
“The Great Way is not difficult for those who have no preferences. When love and hate are both absent, everything becomes clear and undisguised." Verses on the Faith Mind, Sengcan