Why are CN readers so bloodthirsty?

The fun thing is MC and his comrades are usually the same ROFL 

Because it generally takes place in a more brutal, unfair society with very different outcomes for showing mercy. In Western  stories, the enemy is often thankful that the MC didn't kill them or at least knows to stay away... but nine times out of ten the enemies in xianxia are complete scumbags who aren't going to be grateful that the MC let them go -- they'll just come back and keep trying with more numbers. The average enemy in xuanhuan is a crazy, arrogant murderous bastard backed by more crazy, arrogant murderous bastards who just come one after the other owing to their pride and / or loyalty to their organisation.

Also, remember that these stories aren't set in a modern world where you can just run to the police and these people will get locked away. So xianxia / xuanhuan readers get used to looking forward to the MC massacring (a) people who've got it coming or (b) people who're gonna cause problems later if they aren't killed. It's the same way that lots of readers wish Batman would just kill the Joker because you know he's getting out and you know he's going to murder more innocent people.

There are of course batshit crazy xuanhuan MCs (like early MGA Chu Feng) so if you're talking about those guys then I understand completely. It's just crazy to destroy someone's family/sect when the others haven't done and aren't planning to do anything to you. 

I agree it totally pisses me off because as at 5 years ago when I started reading light novels I always invest myself emotionally in the story seeing myself as the mc so if the mc was said to be evil and ruthless I expect him to act like one but if he was the righteous type I expect him to behave accordingly. It wasn't until 9 months ago that I started reviewing all the tons of novels I read and then I realized all those authors have been taking us for a ride and mocking our intelligence.
Imagine a MC that was murdered by some chick he had no grievances with in his past life , after been reborn swears to the heaven he will find her and then kill her thats the was about to be killed by another chick he didn't offend in the current life but he will later risk his life to save her even offend lots of influential young masters while doing it 

Logically if someone threatens your entire loved ones, you are not expected let them go 

that's if the person on question is a male when it is a female the mc will just ignore it. I remember one where the mc was the former medical sovereign before he died and was reincarnated . he was nearly killed by the younger sister of his teacher and the teacher in question is realms above him in terms of cultivation (he was refining pills in her room and might i add she literally threatened him to refine the pillwhen he succeeded she was so happy she cried the moment her younger sister walked in she instantly tried to kill her he was lucky to survive. She wasn't sorry neither was she remorseful 20 chapters later she tried to kill him again but the mc keeps giving her god tier pills cultivation techniques and teaches her cultivation this is the same mc that cripples people for talking back at him 

Well, sometimes I wish the MC wipes some clans, but in general, I think that most of the readers that wants massacres all the time are the new ones that likes these novels full of clichés. I have been reading novels for years and the common one no longer pleases me, after reading some masterpieces, the novel is no longer just about killing but more about the protagonist's Dao(path). 

It is not even about laws, chinese novels - not all but a lot of them - consists the most petty characters in the world that have god like powers.

Though I read about pre three kingdoms time in China it was not that different from the sh*t happening in xianxias lol 

Yeah and they eat up "10,000 Year Old" plants like they were mass produced. I remember one series Duolo Dalu I think that covers a few generations, due to overharvesting of the spirits for spirit rings, the next series/generation all end up having to use other systems because they got farmed to near extinction.

"Look!! A 1,000 year old Ginseng! If we waited another 9,000 years it will become an immortal treasure!!!"
"Nah, no time, I can't wait another 9,000 years *chomp!!!*"
-No more future 10,000 year old Ginseng-