Why do people hate on some uncoman mix breeds?

I see and hear people all the time who make fun and call my dog a filthy mutt and comes from a BYB and has major health issues when I say my dog is a Chin-poo. A japaneese chin and a poodle mix. We recieved her from the American puppy club and her vet said she has the best hind legs than she has seen in a long time. I'm just wondering why people are willing to make theese snap judgements? Please don't be rude I am just wondering...