Eh didn't want to chime in on this, but.
You guys are missing the reasoning and point of this. It's not about censorship, the reasoning anyways. The reasoning is something that very much took place in America, and like Japan always is, they're 2 decades slow.
The idea is that, Japan's young adults are a bunch of worthless losers that cannot give up "kids things". Cartoons, comic books, and video games. Sound familiar people? These things are attached and associated with children and are frowned upon when you're an adult. America started stepping out of this recently. For you children that weren't around in the 70s, 80s, and early to mid 90s; you were pretty much a loser/nerd/geek/pathetic waste of time if you did any of those things post grade school. Playing video games in high school? What a pathetic loser! Comic books? HAHAHAHHAHAHAHAHAHAHAHA. But today hell, people in college and adults talk about Death Note and Naruto. Which I find really ironic since both of those are for children(ages 5-14).
The funny thing is, most anime/manga are aimed towards children to young teens still. And people in the JP gov't think that adults need to grow the hell up and move on pass their childhood status of cartoons/comics/games, and think this is a good idea to force them to grow up. You know, by moving pass semi-perverted/perverted cartoons, and get REAL PORN!
The law in essence is dumb, and the reasoning although legitimate 2 decades ago, is kind of ridiculous now. Oh Japan, when are you going to catch up?