I don't know if I would be comfortable rehoming. With this type of dog all it would take is one time and they will have killed another animal. I wouldn't put it past this dog to kill a small fluffy dog either. I couldn't with a good conscience rehome this dog, because if it killed someone's pet or other dog I know I could have prevented it. You can't keep a dog isolated for the rest of it's life, it's just not physically possibly. It is going to come into contact with a small animal or another dog at some point.
Working in rescue as I have for years, I can tell you that dogs that are dangerous to small animals and occasionally even other dogs are not considered a liability for rehoming. ANY human aggression (provoked or not) is, but inter-animal issues are a very common thing and regularly dealt with by most reputable breed rescues, especially those for large, strong-willed breeds. They know the issues, they know the solutions, and they have a huge network of people who know how to manage dogs that don't 'get along with everything.' In fact, getting a dog that did get along with everything into rescue was a bit unusual.
Both of my dogs would happily catch and kill cats and squirrels outside, and one is also dog-aggressive, yet they live peaceably with my housecats and all dogs that I choose to introduce them to from pugs to huskies. Obviously these dogs can NEVER be allowed to roam loose, but you don't need to socially isolate them at all. You just need to keep them on a leash when out and in the house or in a well fenced yard when unsupervised. Most importantly you need to train them to behave politely in company. There is a rare dog that is irredeemably aggressive, but over 90% of the confirmed cat/chicken/squirrel/rabbit/guinea pig/bird killers I worked with and placed went on to live happy lives with happy owners. One of them actually became a police dog, which was really cool.
That is not to say you're wrong- it is a very personal decision on what you would be able to feel okay with and sleep at night after. Everyone has to do what they feel is best, and there is a risk they might go back to their old ways, especially if the new owner is not competent. Just like a bucker or kicking horse- they need strong, smart people who will maintain the right environment and discipline.