That's ridiculous, 15 years and $250K? What the hell are they trying to prove, that they're as fundamentalist as the Catholic Church in the 1600s? It's a comic! He didn't stalk, touch, rape, or look at real children in lust for all the evidence that is.
Okay, I can understand why he would take a deal. It doesn't matter what the law is, if a jury already thinks you're a pervert they'll lock you up for anything that's on the table. Now, because he's into manga, he's going to be strung up to a polygraph and be subjected to a psychologist prodding into every corner of his life to find out what made him decide to veer from the norm.
Yeah, it's weird that he's into child hentai and bestiality, and I'm not endorsing it, but there are droves of people who are plenty worse who won't get caught because they keep it online. If the postal service hadn't been rifling through his mail it would never have gone public and this guy could have lived his perfectly normal life. Nobody deserves to have their dirty little secret revealed.