I think many people understand why he did it. They still don't forgive him because in doing what he did, he ultimately put Saegye in the same situation as he was throughout his life. And let's face it, Saegye's life wasn't all rainbows and sunshine. He was also going through stuff with his family not being able to trust him.
I also guess they hate the way he did it. I mean he could have done it in a more quick and painless fashion, like force-kiss him or something else. But he chose to get close to him and let Saegye feel vulnerable with him and then ultimately broke his trust.
That's the kind of shortsighted answer I dislike the most. I'm pretty sure there are people more than 14 years old who hate Jinsol. I've read and watched my fair share about psychos and I still hate Jinsol.
Even if people can empathize with what he has done, he manipulated someone who was as broken as him.
In this world context, even Saegye is bad (not like the dare killer, but still) because of his lying skills, but he wants to survive. For 30 chapters, we have come to see Jinsol being "caring", saying repeatedly that he "loved" him. Saegye being reluctant to like him began to shift his interests from the blond guy to Jinsol. And when Saegye started to depend on Jinsol, he betrayed him.
I didn't like Jinsol from the beginning because he was too shady, and I need his redemption arc to forgive him. Even if I understand his part of the story, I can't bring myself to like him.
I find the story really compelling and the setting is pretty much original. It's like a dystopian approach set in modern society. Every character is fleshed out. The author did great job.
Idk why so many ppl hate jinsol. He did what he needed to do and tried to discard his feelings but thats hard to do since he's a highschool student who literally killed his father to save his family who didn't even trust him for half of his life. Its obvious he regrets what he did to saegye.