I've always used the idea of an act such as that as a piss take for whenever we see hacked boxes that is clearly the users fault. Obviously such an act would never come into force and nor would I support it (except on 1st April). On the whole theft of details business I'd disagree over it being worse to steal details than making them available. Banks are always blaming their customers for leaving details in bins and so on yet when they make such a monumental fuck up all they do is get the person prosecuted (good thing, I'd agree) and quite happily sweep it under the carpet. They've made it easy for someone to do it so they have. Crime pays, however the cost to the criminal also increases as it gets harder - Organised criminals are bussinessmen - if it doesn't pay well enough they're not going to do it.
So going back to your anology of leaving a car unlocked (with the keys in too?) would you get any sympathy from the Police or insurance company? Oh no, you'd be laughed out of the building and charged far more on next years premium. Sorry, thats wrong - you'd lie and make a claim increasing everyone elses premium.