What do "emotional support dogs" do?

my sister lives in a public housing development (low income). i visit her often and ever since she moved in i have always wondered why there are so many pitbulls in her housing complex. pitbulls, rottweilers as well. you're allowed pets in her complex but you're not allowed those type of dogs. there are weight and breed restrictions. today when i went to go visit her, her neighbor was sitting outside with his dog (pitbull) and I asked him politely how he got away with keeping the dog and not getting evicted? he said the dog was his "emotional support dog" and HUD can't discriminate against an emotional support dog based on breed. he also said that most of the other people who have pitbulls in the complex have their dogs as "emotional support dogs." he said all they need is a letter from a therapist or psychiatrist. now, i have nothing against the breed. but this neighborhood is beyond below poverty, most of these people with "emotional support pitbulls" are breeding their dogs together and selling puppies out of their house. the complex is FILLED with pitbulls and it doesn't take rocket science to realize that most (if not all) of these dogs are just pets. I'm pretty sure if I asked my therapist to write me a letter for an "emotional support dog" she would. is it really that easy to play the system? to make it harder for people with legit disabilities to get housing with their dog? what a sad country we live in.