Cultivators aren't suppose to interfere with mortal politics, but I wonder how defined the line is. Actually fighting like A-Ting did is considered a crime by Kunlun, but she did stop the general from being poisoned. Also...Qu Chen's master gave the actual emperor a life extending peach and a magic drum, and then kidnapped his son.
The one constant I've seen, is that if one has enough fame / infamy (nearly always based on power), they can do what ever they want, like kidnapping the prince and forcing trash on mortals as a tribute. Tribulations themselves are supposed to represent fighting the will of the heavens or some higher realm. So, I think the "don't interfere in the mortal realms" is more of a courtesy that is only enforced if caught and if they can be handled (ie. less powerful). Kind of wonder if A-Ting can join in on the fun, by trading skills for something minor, like a flower from her grandmother.
The sects, in my mind, are more or less roving mercenary groups that enforce their own rules, and can't be fought against, so they are considered something akin to natural disasters for mortals.