Well you can think of this in that way: In CN novels there Exist the New Term called "Face". If MC offers someone who has a "Face" (Pretty much all have it) then they have to retaliate, cause if they let the one who harem they Ally/underling/far of Relativ of they would be a Joke. Like "He cant even take of his underling Hahahahah". And ever if said enemy of MC is doing something that the Elder of their Clan dont allow, they would let the said Enemy do it and at the End Punish themself. So Pretty much 1. MC cant harm/offer or dont give "Face" to the Enemy. 2. If Enemy´s Underling cause any Harm they themself Forbid, then MC cant stop it, cause they cant show Weakness and let a outsider stop him not can they let other´s know they let one of their own would do something lowly like what he is doing (Often Rape or kill Commoners) so they let him finish it and then Punish the one with the Family/Clan Rules (In Evildoer´s case just dont go Public till the Whole thing is over). And to kill the Rest of the Clan/Family is often like this: If you dont kill them all off they will Harm the Ones around the MC, cause if MC only kills the Main Evildoer the Elders of said Evildoer will take Revenge, cause they cant Let someone get away with killen one of them without retaliate to the MC of they would have no "Face" left. The Term "Face" is pretty much they Pride.