There very well may be bad dogs, like people. If that is true, it is much, much rarer IMO to be born a bad dog then a being born a bad person. Have you read up on the Michael Vick fighting dogs? Almost all of them went back to being the faithful, beautiful dog that they were born to be. Almost all found new loving families, and almost all dogs returned the love expotentialy. There were a few dogs(3 if I recall right) that could not be rehabilitated, and had to be euthanized(perhaps born bad dogs, or perhaps suffering irreparable mental duress from fights).
https://stories.barkpost.com/vicktory-dogs/