Theres a spectrum too it. Helping design fighter jets and missiles? Yes that has to be done with the idea that the weapons you are designing for national security can and most likely will be used in such a way that will cause harm. However in espionage or cyber security, those are almost all pure good. You are protecting information or attaining information.

The main myth though is that somehow there is this idea that someone working as a booze allen contractor for the NSA or CIA is going to now be blackballed by everyone out of disgust. Most people will see it as good, and most companies just want talent and dont actually care about what areas people are in.