When I was a kid I lived in a remote place. No McDonalds, no theater, no mall, no doctor, no vet, lots of dirt roads, no sheriff on Sundays, etc. When we had an animal that needed to be put down, we used a shotgun. The place where I now live, that is illegal, but when you are in a place where you have to take care of your pets the best way you can, you do what is best with what you have.
Sometimes that mentality doesn't change despite far more humane options being available. In this case, a bit of education might be a better approach rather than the knee-jerk reaction of causing harm to the person drowning the pet.
Sometimes a person has never experienced love and they don't know how to treat an animal, another person, or even themselves with love. Such a person may not fully comprehend how atrocious drowning a pet really is. Responding with violence should be a last resort when possible. Despite committing such a horrible act, not everyone who drowns an animal deserves a beating.
I'm not saying drowning or a shotgun to the head is OK; I'm trying to give another side of the argument is all.