Yeah, I do see your point. But from what I understood, it isn’t exactly a new concept that servants historically had very little power to refuse or go against their masters. The Cursed Boy himself knows what it’s like to be powerless and have no real influence, so I kind of expected him to understand, at least to some extent, that Kwon isn’t really in a position where he can openly oppose his master.
Also, every time we’ve seen Kwon interacting with the brother, he’s never seemed willing. Even in the current chapter, he was telling him to stop. And unless I’m remembering it wrong, the Cursed Boy heard those interactions too, so he knows Kwon wasn’t exactly a willing participant. From our perspective, Kwon has always come across as reluctant rather than complicit.
That said, I do understand that the Cursed Boy is acting out of incredibly strong emotions. He’s hurt, betrayed, and desperate, so he’s probably not thinking about the situation completely rationally.
I just personally find it a bit extreme that he chose to curse Kwon instead of his brother—the one he knows is deliberately and willingly hurting him. With Kwon, he can’t even be certain that he’s betraying him of his own free will.
I just feel so bad for Kwon. (The Cursed Boy too, of course… but still.)

But isn’t it obvious that kwon is being forced? Like kwon has zero power or position. Why would you curse him instead of your brother??