This is one of the areas that I get upset with.
Normally a person does not tempt a stalker, or gets harassed, on the Internet unless there is some sort of provocation. I stay clear of chat rooms - the closest I come to one is when I am playing games in Pogo!
There are ways that you can protect your identity. There are programs available to make you computer "invisible" to others which would stop the stalking or the harassment. You can always switch your ID when you go into chat room areas (i.e. never go in under the same ID twice) if you must really want to visit the chat rooms.
As far as things like MySpace and FaceBook, be leary of who you allow as friends. There are capabilities with both that allow you to block a person.
As far as offenders, I think it would be really difficult to really do much about them. Only because the victim allowed them the access to begin with.