I think the driving force is that he isn't exactly loyal to the king, he follows him because Karas is very objective when approaching his goal. Karas doesn't let human emotions have a factor in his decisions that is why he is effective (and very cruel). Kin must've seen that as Karas' strength and the way Karas can now be swayed by Abel's influence can just change the tides in Karas' decisions. He is already tweaking his plans for Abel.
It could also be possible that Kin doesn't want Karas to have any weaknesses that the council could use against him. This is from how I understand them at this point of the story. All of the characters are really interesting and I love how you can analyze their thoughts like this.
Yea I agree but also his ideal King is very much nightmare fuelled. Abel realize and know it better than anyone Karas behaviour currently is self damaging and is not a healthy mindset at all. That source of strength is going to backfired eventually, the strengths to protect is always better than revenge
All that first commander think is very much revenge driven, and even trying to sacrifice Abel is just as evil as what that council is doing, but he is blinded by that hate to see it.
Why is he so salty the King finally found his happiness? That revenge can wait, cause they clearly have the same goal wth