End the euthanization of millions of healthy animals

It is appalling than millions of cats and dogs each year are euthanized in shelters. It should be illegal for any healthy companion animal to be killed. The only instances in which euthanasia should be acceptable are if allowing the animal to live would cause it to suffer or if it is so aggressive it cannot be properly cared for or is a SEVERE danger to other animals and people (and no this does not include a dog that bites someone once in self defense).
Please end this senseless killing! Homelessness is no reason for murder! If it's not acceptable to kill people or unwanted children because they have no home, then there's no reason to kill animals for it!