The internet makes harassment considerably more problematic. Even setting aside constitutional defenses of speech, just trying to figure out which agency should be in charge of investigating and prosecuting harassment is confusing at best.
Do you go to your local police? Do you go to a federal agency? Which one? Even when you do approach a law enforcement agency after receiving threats, do they think its worth their time to investigate? (Amanda Hess's piece on harassment is an interesting for her interactions w/ the police alone: http://www.psmag.com/navigation/health-and-behavior/women-ar... )
Revenge porn is an analogous (but not identical) problem, and even in that case, where basically everyone can agree it's a bad thing, it's clear first that states don't have statutes which they can use to prosecute (until very recently at least: http://en.wikipedia.org/wiki/Revenge_porn#U.S._laws ), and in several cases some of the laws being written are complete clusterfucks.
The truth of the matter is that you can get away with a whole lot of bullshit before anybody starts trying to drop hammers on you. And harassers live in that space between what is legal and what is enforceable (a lot of other interesting stuff lives in that space too).