In Transfiguration, students learn to vanish animals; snails, mice, and kittens. In the seventh book, the entrance to Ravenclaw tower asks where Vanished objects go. McGonagall replies they go into nonbeing, or everything.
“Where do Vanished objects go?”
“Into nonbeing, which is to say, everything.” replied Professor McGonagall.
“Nicely phrased,” replied the eagle door knocker, and the door swung open.
Deathly Hallows - page 501 - Bloomsbury - chapter 30, The Sacking of Severus Snape
Assuming McGonagall is correct and "objects" refers to anything vanished, living or not, wouldn't causing a living thing to go into "nonbeing" be tantamount to killing it? Obviously what happens after death is unknown, but vanished things would lose their being and probably their consciousness.
However, after the class tries to vanish mice, a "wriggling mouse tail" is all that is left of one mouse. Vanishing something is different than making it invisible, but this implies the mouse is still somehow controlling its tail, consciously or involuntarily. This doesn't seem to make any sense if the rest of the mouse has gone into nonbeing.
But all in all, wouldn't taking away something's very being, especially something as sophisticated as a cat (and more powerful wizards could probably vanish even more sophisticated animals, maybe even humans), be considered taking its life away? Is this not considered equal to killing? Would it not be regulated at least?