What is the difference between a UGLY mixed breed and a purebred?

I'm not sure if I understand why people are so hard on mutts and mixed breeds. They are dogs, and dogs are dogs. I have a mixed breed who is a mutt, and she loves to play with my purebred dogs. I have a mix of purebred and mixed breeds.<br><br>I understand that breeding is a business, but why would mixed breeds be viewed as lesser than purebred dogs? I just don't understand why people would think that a mutt is lesser.