How did you come to the conclusion that this was the intention of the devs? Not an attack, just a question.
Although there are plenty games that do fit that description, there are also some that don't.
I personally have the feeling that the devs wanted to make something more than just escapist porn.
I generally use the tags and the synopsis to try and understand the game. Most games with any sort of tough to digest content does present the tag with said content. Additionaly, some devs make an extra spoiler detailing warnings for certain content. Since this one was detailed as a Romance and none of the tags suggested anything like this, it gives the impression of a soft game.
Furthermore, at least 50% of the game you have no idea this is coming towards you, it's a pretty wholesome experience getting to know the girls and watching the relationship between the MC and Haley blossom. This is just dropped immediately after they have sex for the first time, literally imediately.
This suggests that since the main seduction had just occured for one of the paths, the dev didn't know how to have any drama remaining for the rest of the game and ass-pulled the whole situation to add some spice very late in development, hence why it seems so out of place.
Everyone can justify things however they want in their own head, so I know nothing I'll say will change anyones opinion. I just comment in the hopes that devs and prospective devs for these stories don't fall into the same traps. I would like if this trend would stop happening in 90% of these Harem games - this mediocre drama over something that the dev feels they need to add when the story seems to become more stale.
EDIT: I almost forgot - another proof that this wasn't really plan was how it was resolved. In a pretty rushed manner, no real discussion is viewed, it never seems like Haley opens up about it we are just left to wonder what happened and what she said to the therapist. The MC isn't really any help to her and, since we know and the MC knows what happened, the whole "daddy" thing feels bad for both us and the MC in-game (he tells her not to say it a bunch of times). So the whole daddy thing we had going on gets ruined as well.