......Made absolutely no sense. First off, he knew that someone was killing people heartlessly to get to him but yet he involves a complete stranger, a stranger who is a woman , who could end up dead also. Secondly within, I'm guessing, 12 hours he completely forgets about his girlfriend who was brutally murdered and decides to sleep with this stranger and this stranger decides that this man who kidnapped her Is hot enough to sleep with as well. It just seems so forced and out of place and didn't match the depth of the rest of the film.
The Joe Turner character was not a villain. He was not predator. He was not a rapist. He was not a bad person.
He was a victim of a government conspiracy which was actively working to murder him. Agents were hunting him down and closing in, he was about to be terminated in cold blood at any moment. He was desperate, he had to do something to survive. He had virtually no options. His best bet was to choose the first random most convenient person he could find and use them to buy some time in safety so he could collect himself and his thoughts, and figure out a plan.
He kidnaps Katherine. He doesn't ~want~ to, he doesn't enjoy it, he isn't getting his jollies. It's an extreme measure in the interest of his survival. She assumes, as any reasonable person would, that he's probably a psychopath who wants to abuse and harm her. She's terrified, as any sane person would be. It sucks that she's put in that situation and obviously she deserves sympathy. But so does Turner. After spending a little time talking to each other and him having a chance to explain his situation, she realizes he's not a bad person, she empathizes with him, she sympathizes with him, and she comes to trust him and wants to help him. They bond and get it on. It's a Hollywood movie, so naturally it's about the most handsome man in NYC kidnapping the most beautiful woman in NYC.
It was 1975, the singles bar scene was at a fever pitch. The concept of two strangers meeting and then having sex within the hour was totally normalized at the time. It probably would have stayed normal if not for the whole AIDS thing, that put a stop to it real quick. Also, the dialogue in the script makes it pretty clear that Katherine is not in love with her boyfriend. When they talk on the phone he comes right out and says he's tired of her always blowing him off and assumes that's what she's doing. And maybe it's just me but I never got the impression that Turner and Janice were exactly head over heels for each other and counting the day til their wedding. They were co-workers who dated and fooled around. He was shocked and sad when he found her corpse but he didn't go emotional super nova over it.
This is pretty much how I feel. While I think the love subplot is a little contrived (it IS a Hollywood movie after all), it's obvious the quick hookup is due to a mutual desire for a brief psychological escape from a nightmare scenario-- Joe is literally running for his life and wants someone to trust now that everyone he worked with died, and Kathy is similarly suffering from emotional alienation and loneliness in the glimpses we get of her private life.