Sorry for two top-level comments, but I did some more reading on the case. It started when the postal service seized a box containing the books. So if there's someone you don't like, just order a few books from amazon.co.jp for them, and then they'll be facing 15 years in prison.
Now you're getting slightly hysterical. They would just claim that they didn't order the books themselves, the evidence would back them up, and they probably wouldn't even be prosecuted.
Plea bargaining is one stage of prosecution, intended to avoid a trial. If they don't get prosecuted (for example because there's no evidence that they ordered the books), there's no plea bargaining.
Plea bargains are not unique to manga-related crimes. If your claim was accurate, it would be easy to get someone locked away for any crime just by planting weak evidence against them.
"Land of the free," indeed.