I think there's a difference between owning a "dangerous" or "vicious" dog and owning a "problem" dog. I also think there is a big difference between owners. I had a wonderful foster border collie. She had a problem with strange dogs. One potential adoptee had never owned a dog before. Another potential adoptee had owned dogs for years and have done obedience, agility, etc.
Guess who I adopted the border collie to? I had a sweet little puppy come through a couple weeks later, called the adoptee and said "I found your dog, come and get her".
Both dogs were loved, well-behaved, cared for, etc. Both adoptees were happy with their dogs. I got two lifetime homes for two fosters.
Had I reversed those two dogs, I would have had the border collie come back and would have turned off the person from having a dog. The puppy was going to be fine in either home.