you have a very poor understanding of the law. anyway, someone did pretty much what you suggest and busted his HDs when the feds showed up. they convicted him for 20 years or something still, though, because of a single poor resolution thumbnail left behind in a Thumbs.db file on his "clean" computer.
downloading CP is definitely illegal. the guy above was busted when the feds set up a "click a link, go to prison" type of sting operation.