I think this is retarded. It's not so much that I have sympathy for rapists and molesters, but apparently peeing on a tree in a park is enough to get you put on some trumped-up list of "sex offenders". Why aren't offences just offences, anyway? If you say something is a "hate" crime or a "sex" crime, all the alarm bells go off. And if you're burning down synagogues or raping people, sure they should. But the second sphere has ballooned to the point where someone can accuse you of looking at them the wrong way and potentially ruin your career. (Fortunately some are starting to see false accusations as a new kind of sex crime, but more needs to be done to "normalize" the charged environment that we live in.)
But let's say that these alleged criminals are using their journals and other social networking in a way unrelated to their purported crimes. What purpose does it serve to take away someone's means of expression and treat them as if their thoughts and feelings don't have a legitimate place online? I just don't buy it. If someone's use of your service violates your TOS, then do what you will. But here the NY Attorney General (which is an elected position, and this position's previous occupant was Eliot Spitzer) is getting a cheap unearned "victory" which he will promote to no end when he's up for re-election.
What's next - do we prevent criminals from reading books? Y'know, they might get ideas and be tempted to communicate them. And we all know that any idea from anyone accused of committing a crime has to be garbage, right?