The film could be paired with THE SNIPER to show the differences in tone and approach toward "social problem" subject matter in the two films (whose release dates are half a decade apart). In THE NIGHT RUNNER, the buildup toward the violent scene is low-key, and it's a single act, as opposed to a murder spree. But at the end of each film, both characters have been rendered inert by an overwhelming awareness of just how dysfunctional they really are.
I certainly agree that the father's actions were rotten, but whether he should die for his actions remains very problematic. How do we quantify the probabilities of such an extreme outcome? For every ten cases of such cruel, intolerant pre-emption, what occurs? One killing, maybe; two or three instances where the daughter finds out what her father has done, sides with her lover, and the two walk off to start a life together elsewhere; and six or seven instances where the wronged party moves on, recognizing that the deck is stacked against him.
However we try to quantify such a sequence of actions, it's still clear that Danton's character doesn't have to kill the father...and his later "reasoning" about his actions (in the somewhat hard-to-swallow confession scene with the daughter) demonstrate that his decisions are flawed by a form of mental illness that is alluded to in the opening scene of the film, when the psychologist is bullied into releasing Danton's character back into the world prematurely.
That's the deterministic "hook" for the film, setting up a noir character dynamic that overlays into a low-key variant of the "social problem" melodrama.
And the noir-o-meter actually captures a good bit of this hybrid dynamic, rendering a character element score that is solidly in noir territory (6.5/10 on the scale), but with the overall balance of the elements tilting strongly toward melodrama. The triangle character structure is clearly here, even if the father is more peripheral to the bulk of the action than the love couple.
Frequent IMDB reviewer Doug Doepke has some useful thoughts that add context, including the speculation that THE NIGHT RUNNER, in a manner analogous to what's often noted regarding TOUCH OF EVIL, might have had some influence on Hitchcock when it came time to make PSYCHO. Here is a snippet from his commentary:
The film's not a minor gem: that would be too much of a stretch. Instead, I think Danton's performance manages a level that truly disturbs, especially with the tight script and noirish background. Catch the occasional little motion or grimace betraying Roy's (Danton) inner turmoil as he struggles with a society full of minor pressures. It's a carefully calibrated performance that shows how an emotive "more" can be expressed by a judicious "less". And since Roy is basically a likable guy, his plight becomes doubly affecting as he tries to blend into a normal life. That last lonely shot of him is, I think, one of the more disturbing to come out of the generally cheerful 1950's.
On a different note: I suspect Hitchcock, also at Universal at the time, caught this minor production since the project bears certain key similarities to PSYCHO (1960). Consider, for example, the roadside motel, the disturbed personality, the brutal murder, along with the symbolic use of birds, in this case sea gulls. Nothing really hangs on the comparison, of course, except maybe the notion that a widely acclaimed classic managed to grow out of an obscure seedbed. Anyway, this little oddity has its own peculiar virtues, so catch up with it if you can.
And, fortunately, catching up with THE NIGHT RUNNER is now a much easier proposition...