All right- first of all, in many places in the US, it is mandatory for sex offenders to register with law enforcement so that they are tracked, so the notice he received is just a part of the process. In some communities, these types of offenders aren't allowed to live within a certain distance of a school, day care, etc.
Second, historically, these folks just don't rehabilitate. They re-offend, and having one in your neighborhood is certainly cause for some concern, especially if it happens to be the kind of victim he/she has had before. No, not every one of them re-offends, but aside from theft, this is one of the most habitual crimes you'll find.
And Hung, you're comparing apples and razor blades, there. Having someone who drinks all the time and gets caught for it is VASTLY different from a predatory criminal that seeks out underage people to satisfy his sexual urges. It's more akin to finding out you have someone in your neighborhood that killed someone, or if you had a known apartment burglar move in.
In any case, it's pretty much law here in the US that sex offenders register, and that when they move somewhere, locals get notice of it.
I would agree that each case has its own details, but we all have our own demons. I don't much like gangster wannabe drug dealers, and I had the most serious run-in you can have with one of those. Unfortunately, unless you know what you're looking for, those remain kind of invisible in the neighborhood.
H
its horseshoes and handgrenades when it comes to sexual predators fuckin wit your loved ones.. ya heard?!! 
