The anxious, existentially befuddled male is at the heart of film noir. Caught in a trap that's not always of his own making, but almost always worse than he deserves, he stumbles around in a maze with no exit. Sometimes he's destroyed by a powerful female, against whom he has no defenses, sometimes he's saved by a powerful female operating out of unaccountable charity. In either case, the situation is ultimately out of his control, which on some level makes each type of female equally threatening.
Some people have located the source of this paradigm for male anxiety in the new economic status women achieved by entering the workforce in large numbers during WWII, but this is a very superficial explanation for the mythology of noir. Eddie Muller, probably the best and certainly the most entertaining commentator on film noir, points out that the good girls of the tradition are almost always working girls, while the femmes fatales are almost always looking to get something for nothing, and certainly not a paycheck for an honest day's work.
The male anxiety embodied in the tradition clearly derives from a deeper source -- the moral discombobulation of war itself, the spiritual exhaustion this particular conflict induced, and the inconceivable fact of the atomic bomb which raised moral issues and created fears that the human psyche was ill-prepared to engage.
The ravaged psyches of Americans in the aftermath of a "good war", a good war they won, so vividly explored in film noir, in some ways says more about the nature of all wars than any works of art which dealt with the conflict itself.