Great question, one I have often pondered. I came close to such a decision a couple of years ago.
I was hunting this area with my dog. She was on the other side of a ditch. She was an area that was covered in short grass and light scrub. Anyway, she all of sudden came to a stop. There was something in her path, the way she acted, it was something unfamiliar to her. I decided to cross the ditch to see.
What I saw was a shock. No more then a twenty feet in front of her was a badger laying up next to some brush. All I had was my 20 gauge loaded with 8-shot. Yes, at that range I konw a blast of bird shot should do a critter in. I did raise the gun and point it at the badger. The badger was completely frozen, I know that they can quickly change attitudes with dire consequences to both man and dog. Then another thought crossed my mind.
What if I shoot and the shot isn't immediately fatal? My dog might rush in and then I would be rushing my dog to the vet' if it survived. I backed myself and the dog up slowly. I have no idea where that creature went and I don't care.
I still wonder to this day what prevented that badger from attacking my dog. I am grateful my dog had the sense not to attack it.