In 1939, the British killed 750,000 of their own cats and dogs, roughly a quarter of all pets in England. When WWII began, a British government agency advised people to euthanize their pets. And they did it, in huge waves! Some even bought special guns to do it at home. Nobody force them to do it. They did it "out of kindness", because if they hypothetically had to evacuate, the pets might get left behind in abandoned houses, and that would be inhumane .