And again, upon realizing (in the instance where it is) that said person's work is leading to *potentially* nefarious consequences (upholding/extending Nazi Germany, developing the A-bomb), another decision/estimation has to be made: are the consequences of my work leading to necessarily nefarious consequences?
In the case of Nazi Germany, the answer would have had to have been, "yes."
In the case of developing the A-bomb, perhaps the answer is a bit more debatable -- especially if you accept the notion that the A-bomb saved lives. This rationale is almost one you have to accept *overall* for weapons development. Undoubtedly if the US's weapons proliferation had been at a slower rate than the USSR's, then we might be speaking Russian right now or at the very least communism might have spread extensively. Certainly, developing weapons that are used to halt the spread of communism would not be a nefarious exercise. Whereas perhaps developing weapons with the intent of spreading communism might have been.