Shu Shan is a sect that is highly respected for vanquishing evil. Which is why most of the people there act like their so superior. They do abuse their power and authority at times in this drama. However, considering that there is a strong hatred between the demon realm and mortal realm, it's understandable that the Shu Shan disciples have a mind set on all demons being 'evil' or a threat. Because demons honesty have the ability to harm humans at wish, so far most of the demons they've encounters in the mortal realm aren't the friendliest.
Plus, they're probably to proud to admit their mistakes of harming an innocent demon or truly being sorry for it but I think they would so something to take responsibly for it, if it was very serious.