The Killing of Animals in its many aspects

[godwulf]

To admit the need for such justification is to assume that there is some rule which killing animals for food appears to break

The taking of a conscious animal life is not automatically or by default a morality-neutral action, simply because someone who wants to do it chooses not to want to think about it.

On one side of the equation are the indisuputable facts that an animal feels pain when shot, and that the animal wants to live; unless you've got a reason to consider those things to be relatively unimportant - or which, in other words, overrides the facts noted - then I would think that the rule of common decency, if nothing else, is something you might want to consider.