So basically under your proposed rule, someone could download as much child porn as he wanted in complete safety as long as he made sure to keep his wifi unprotected? Your rule needs some refinement! :-)
I implied that they could be more civil if there is a chance that the owner of the internet connection is not the criminal. They could knock on the door, politely ask the owner to answer some questions and do the rough stuff after they are absolutely sure that that guy is the one they are looking for.