Joker does not have any depth and that's the great thing about him. He just likes destruction but people keep trying to rationalize, even justify why he's the way he is.
I think The Killing Joke had the best interpretation. It's boring if he's just 'crazy'. He's clearly not. His intention is to prove that chaos/craziness is a factor everyone should be aware of.
A truly chaotic person wouldn't predictably choose the route of "violent chaos" every time. They'd do other shit.