Why do people hate pet stores

I dont understand this. I bought a perfectly healthy pup from a pet store. He is 2 years old now and he is one of the best dogs Ive met. Ive been to that pet store many times. All of the puppies are well groomed and are clean. Yea, there are a few timid ones and a few mean/hyperactive ones but most are perfectly active, compassionate, and playful with the other dogs. The store will let you hold a puppy and they have rooms around the store that you can go in and play with them. My question is why do people say that ALL pet stores get their puppies from puppy mills? Yea I know they get some but not all of them. Also they say to NEVER buy from a pet store, adopt, buy from a breeder, or somethin. I just dont understand. Also is it just me or do people need to shut thier freaking mouths about this pet store issue?

Well you got lucky, my baby girl that is sitting right beside me, is a pure bred doberman purchased from a pet store, with assurances, but she has hypothyriodism, meaning medication for the rest of her life, generalised demodictosis (uncurable mange) that cant be treated fully because of the hypothyriodism, she cant have antibiotics, her immune system crashes as soon as the course is finished making her worse than why she was taking antibiotics, she cant be spayed, the vet wont run the risk of even this surgery, i have to monitor her blood sugar levels weekly as she is a candidate for diabetes, which combined with the thyroid problem could kill her in months. She is in fact infertile so the standard reason for spaying isnt a problem but possible cancer as a result is. Dont get me wrong, i love my girl and would happily spend that $5000AU again, but i shudder to think what would have happened if someone else had of bought her instead. And the only thing the pet shop said was, 'we are sorry, give us back the dog and we will give you a 50% refund and destroy the dog'. Like hell, i had already spent $500 on having tests run on her and getting back $175 wasnt going to cut it.