Seungho’s childhood

Yeah, your theory seems pretty solid to me.
If Seungho was abused by his father as a child, it may explain his love of sex and debauchery. Like he was initiated into sex at an early age or something...

We can also imagine that he wasn't raped by his father, but that his father just gave him a very strict education; like his father forced him to kill someone for the first time at the age of 5 or some crazy shit like that. In that case, it could explain his psychopathic behavior.

Also, to complete your analysis, I would say that Seungho as the eldest son, is probably the only one who was abused by his father. Look at his little brother, he's perfectly normal.
My hypothesis is that Seungho, when he was younger, made sure his father didn't touch his little brother. He protected him by enduring his father's abuse for him, and that cost him his sanity when he grew up. And now "bearded old men gives him the shudders” .
Pretty creepy theory, but very interesting, isn't it? (=・ω・=)

I can see the strict education part happening

Hear me out. What if the other nobles/politicians his father worked with were the ones that did something to Seungho? And maybe his father was aware but didnt do anything in order to save face and position. Or didnt believe him and when the truth was discovered the fathee had all those nobles framed for treason and that is why only the Yoon family was saved. His father instead of being there for his son, just cast him away like basically victim blaming him for the whole thing.

Oh, yeah, that's a great theory. Maybe that's also why Seungho keeps saying that he has no political ambition and that he doesn't want to be a candidate for a government job. Even though he's got all the qualifications.

Anyway, I'd love Seungho to have a dark past. Without over-dramatizing it, and making him look like a poor victim. Just something juicy to balance out his personality.

All these could be true or seungho might just be a genuine psycho

I believe people are under the impression that being a victim of abuse makes someone weak. Or that sexual abuse only means rape. I had someone say they dont see Seungho being a weak victim that wouldnt fight back. Sure someone can be strong of character, but I believe that whatever did happen to Seungho was since childhood. I can see Seungho being groomed/exposed to sodomy/sexual acts from a very early age. He literally told Nakyum he would tease his servants when he was young by dragging a brush over their naked bodies as punishment. Like, red flag. A kid wouldnt be doing that kinda stuff unless they saw it or were exposed to that type of behavior. And based on the father's reaction it wouldnt seem like he was the one responsible.

" He literally told Nakyum he would tease his servants when he was young by dragging a brush over their naked bodies as punishment. Like, red flag. A kid wouldnt be doing that kinda stuff unless they saw it or were exposed to that type of behavior "

Oh, yeah, I completely forgot about that detail. Good point. Indeed, the hypothesis that Seungho was exposed to toxic and inappropriate behavior at a very young age is very possible.
Also, when I referred to Seungho as a "poor victim" in my previous comment, my concern was that I did not want that to be an excuse for his behavior. His dark past should be used as an explanation, not an excuse for his crimes. I hope that the author will not fall into the trap.

oh yes I believe I misunderstood your comment. Regardless of what his past was ,his current behavior is definitely not excusable. No one has a right to do the terrible things he has done. But it sure is interesting to be given insight on someone's past.