I think it's because people- even sometimes including "dog people" who should know better, are conditioned to believe that dogs must be bombproof to have the right to leave the house. It's not really fair, because how else can you work with a dog who has issues than to get it out and work with it? But- people believe that if you dare take a dog out of your front door and it doesn't love people or other dogs, you are a bad person, ESPECIALLY if your dog was from a breeder. Even in competition, I have heard people rant about "the super reactive dog" (who just barked two or three times at a passing crowd and was totally under control) and how "she shouldn't be taking that dog out in public" and how "she probably got it from so and so who ALWAYS breeds bad temperaments". I didn't know that lady with the reactive dog, I don't know who she got it from or what it's backstory is, so I didn't pass judgement. Its probably just a dog who is a little noisy in high-stress situations. That dog also went on to get first place in its agility class, and was a very cool happy dog.
Why is it, that we expect dogs to be totally subservient? They are their own beings... have their own way of looking at situations, and don't understand the world from birth. It is our job to teach them how to handle situations, but I don't think there is anything wrong with a dog who never fully handles a specific situation either. It's like, getting mad at a kid with autism because it doesn't act the same way a "normal" kid does. Dogs are not robots, and they think for themselves! We have to accept that our world is a stressful place and that not all dogs will handle it well.