Perhaps you should get involved in trying to help change some laws if this is that big an issue for you.
Because as it stands and rightfully so (IMO and I am mentally ill and have been "Insane") being stupid is not even close to being insane. Living a life having never been called out on or forced to face the consequenses of ones illegal or immoral acts is not insanity. Being selfish and having an obvious ability to shut ones feelings off after being involved in illegal or immoral acts is not insanity. Insanity is about not knowing what one is doing- having your brain work against you, not having a choice, being unable to reason or make sense of the world around you
Your list above? Are not the acts of an "insane" person, they are the acts of the oh SO common stupid criminal. MANY criminals are this stupid and make these kinds of choices. They too get themselves caught.. and most times convicted Often-times all by themselves! The evidence used to convict is left by none other than the stupid criminals themselves- their own LIES, mistakes, lack of planning and activities after the crime is what does them in. Why do you think the prison systems are so overcrowded? Have you never watched "Cops"?
Do you think Scott Peterson was "insane" when he killed and then lied about and covered up his wife and unborn childs murder? He was "partying" after his crime too- his lawyer was quite the clown, was even on TV talking major about him before he took him on as a client! He sat in court chatting and laughing in front of the jury. Ha, He's STILL lying and lying and lying and it's HOW many years later?! It's what criminals DO- they are conmen- some are darn good at it, some get better with practice, but some others (quite a bit of them), can't con anyone but their own enabling parents and end up spending their entire lives in and out of prison.
If Casey did this, if she murdered her child, she is going down (probably with evidence or information she herself left behind) and rightfully so!
Insanity is not so much hard to prove as it is rare. Only about 1% of the ones who do attempt to use it, succeed. It isn't a joke or something to be used lightly on someone like Casey Anthony who does not even have a history of mental health issues.