Why is Hentai Censored in Japan?

I remember reading something about it months ago, but never fully understood.
Who is it censored for? Will there ever be a day where this might change?

if zero is right i reallt fucking glad i live in America, and honest to fucking god, its porn, if censored is 18+ and uncensored is 18+ THEN WTF IS THE POINT, oh customs my ass, they probably dont do it it probably works like this:
Artist takes 3 weeks on awesome Hentai comic -> inker&colorer take a few day shading&coloring -> then before i can be released some faggoty ass prick comes and turns some nice pink into fucking cubes, does that not fucking ruin the whole purpose of hentai?? oh and STFU about "it makes you wonder whats there" ITS A PUSSY/DICK wtf u think its gonna be?? and if you want to see fucking uncensored hentai just goto google images and search hentai or any other porn shit, turn off safesearch and theres your fap material, or people go and get fucking gf and tap some ass, and yes people we can tell by your posts that your basement dwelling13 y/o's so gtfo 4 chan and play runescape, welll back to the point i WAS going to move to japan for tech jobs but i guess i would just need to bring an assload of hentai with me, anyone know of theres some law about bringing porn on a plane or into japan? iight well if you ppl want to know, those who like pr0n vids and not pics watch good old American pr0n (like Lichelle Marie) and those who like pics get really good HQ Hentai pics (i reccomend yuri) with nice view of a puss and you'll be whackin' off in no time. well this post is way fucking longer than i thought so im ending it, bye
~RSR