I know it's not a defence in Victoria, but excessive consumption of alcohol was (not sure if it still is) a defence in NSW. As in "I was so drunk I didn't know what I was doing therefore I'm not guilty."

I know it was in 1997, but I've no idea if it's been changed since then, although I'd certainly hope so.

And in agreement with the alcohol exacerbating the problem. Alcohol doesn't in general help with problems though. *shrug*