because every life, even that of a dog, is worth fighting for.
Agreed, but in reality, the choices are A) adopt dangerous dogs out to people, B) hold onto the dogs for their entire natural life, C) release them onto the streets, or D) euthanize some of them.
A is obviously not ideal; a human getting killed by a dog that they expected to be nice is worse than that dog dying. B would be great if shelters had infinite space and infinite funding, but realistically they have limited space and limited funding. That leaves us with C or D. Stray animals make more stray animals, they attack people, pets, and wildlife, they spread disease, and they tend to die horrible deaths. Euthanasia sucks, but the real alternatives are worse.
The real solution that no one wants to implement is to make it a crime to have dogs and cats that aren’t spayed or neutered, with extraordinarily rare exception. The only dogs that should be allowed to be bred are working dogs, and that should be closely regulated. Your shepherd/retriever mix, however cute he is, should not make more puppies as long as shelters are overflowing and turning animals away.
“But wouldn’t that lead to the extinction of these companion animals?” Be realistic–this law would never catch every single illegal breeder, and it would never prevent strays from breeding. Dogs and cats would not go extinct, they would just stop bringing shelters to capacity and beyond.