This is a common ending of a terminally ill process and apparently seen as humane. Though I think if anyone treated their dog like that, we'd report them for animal abuse.
I don't have good answers to most questions surrounding this topic. But I'd like to get to a point where people are treated as humanely as their pets in their final period. And I can't even tell you the current practice isn't, just that it does not at all feel that way to me.