The issue is that you're punishing the victim. You're telling the victim of harassment that they're no longer able to participate in the community, despite them not having done anything wrong. And while you might not be interested in participating in things like twitter or YikYak, or even here on HN, others are. And it's really not fair to say, "You got harassed, now you don't get to participate. You have to go sit away from everyone else."