Why do purebred dog owners hate mixed breed dogs ?

I never heard anyone who owned a purebred dog say this or even hint at it.  Dogs are dogs and the truth about pure bred dogs is, many of them are neurotic or have health issues because of in-breeding. 

The registered and recognized pure breeds take years and generations to keep them pure and of standard. Some have been from countries that have had them for 100's of years and would like to keep the breed, not mixed and loose the genes. Breeders of purbreds take pride in the litters, show points, pedigree and results from years of showing, caring and seeing the results of the breed. The so called designer breeds are not breeds, just a mixed dog. the Labradoodle, Goldendoodle, Pomchi and more are just a mixed breed and will not be recognized as a breed if at all for years and years. Lots of mixed breed dogs end up in shelters or destroyed. I have a mixed breed dog, don't get me wrong I love all animals, some suffer from the negligence of others.

We don't hate mixed breed dogs. The fact is, we love Basset Hound puppies. 

Because the mix breeds are actually demons, nephilim, they are half dog, half something else 

Hate is a hard word.  If someone spends two thousand dollars on a dog, they know that the dog is the best quality they can buy.  Free of negative traits, free of deformities, guaranteed temperament.

Kinda like the rich looking down on the poor.  Most people can only afford dogs bred by BYBers or Puppy Mills that are chalked full of negative traits, bad temperaments, predisposed to specific illnesses.

A good quality dog is like owning the most expensive car you can buy.  QUALITY.

the question did not provide any  supportive evidence  or sufficient  reason to accept  such a proposition / allegation to be  a truth

what is presented is   a  GLITTERY GENERALIZATION ..an EMOTIONALLY  appealing "PHRASE"  closely associated with highly valued  concepts or beliefs that it carries CONVICTION  by some WITHOUT supporting information or reason .

such highly valued concepts attract GENERAL  approval and acclaim  they ask for approval without examination  of reason  .typically used in propaganda  poster  advertisements  by  politicians  and propagandist

and web pages even the religious  and the  them vs us mentality

I love mixed breed dogs. I enjoy their unpredictability.

I dislike when people try topretemd they are a breed by giving them a cutesie name.

 This  question is very far from the  truth indeed..... i dont hate mongrels, i have owned several. Though i  do disdain the arseholes who back yard breed them,  and try to pass them off as purebred dogs In order to sell them to fully blown idiots.

For the most part, that is a false accusation.

people get what they can afford.