Because everyone has stuff to hide. You dont have to have criminal activity, ongoing or in your past, to want to keep your privacy and keep things hidden. I always counter with "Okay, then lets paint your social security number on the side of your car if you have nothing to hide", and they always stammer and stutter about how thats different and that would cause them no end of headache if someone got it and stole their identity.

And yes, thats the point. You have stuff you want to protect and keep others from knowing. Not just for identity theft reasons, but for social reasons as well.. You probably don't want your spouse to know how much you hate their sibling for no reason, or want your boss to hear what you say about them at home, You dont want people at the bagel shop to know your bank account number and password, Or any of a thousand other things that you do every day, that you dont want other people to know about.