That's an interesting question and as you raise it, I struggle to think when that would ever occur. I think there would be extremely limited occasions. However, I think it's important to include it and that might surprise you.
If for instance and I saw an instance once.... Here's a short story. A service dog, who had been in service for a considerable period of time, was outside in his run during a lightning storm and panicked. We're talking about being inside a well-made, chain-link, very well-reinforced kennel. He broke out of that kennel in a panic, injuring himself to escape this massive storm, and the handler was away. The handler had no idea this was occurring.
If you had an instance when a trained patrol dog engaged me and I had done nothing wrong and the handler wasn't present and I was not able to get that animal to stop hurting me without causing it harm or causing it injury.... I would pray it would never occur, but a dog in panic.... They're still animals. Yes, service dogs are unbelievably well trained. If a hunter shoots a deer it can run for a mile after it's been shot through the heart. How can it do that? A human would never do that, but these are animals and truly they're domesticated dogs but they are descendants of wild animals. In panic, in flight, in fear, if the only way I could protect myself from...and there's no malice because the dog is just terrified. The only reason I could imagine that clause being used is if this animal were attacking me and the only possible way I could survive that attack was by taking that animal's life to protect myself, that would be about the only occasion I could imagine where that defence would exist.
This was a well-balanced, solid dog that had been in our program for a long time. We had worked around gunfire. We had worked around tactical teams. It was some trigger with that storm and all the circumstances; the dog panicked. To see the kennel—and I saw the kennel—to see that a dog could modify chain-link the way that dog did to escape from the kennel, I was blown away.
So that's a short story. I think it's important to have it. I think the chances of there being a lawful excuse for harming a service animal.... If I have to pinch you to let go of me, technically am I harming the dog? I guess I probably am. But if you're biting me, there's reasonableness in my doing something to get you to stop. But outside of that we try to be very careful, very diligent; we work very hard and train very hard to do our jobs as best we can. But again you have humans interacting with animals trying to perform a service.
Could something happen, some untoward, unfortunate event? I suppose it could. It would be terrible, but I think not to give someone the ability to protect themselves from unjustified circumstance is wrong. So I think to have this.... If we never use it, that's fine. We may never use it, but I don't think there's any harm in having it either.