Nice. In fact, network analysis can automatically detect behavioral patterns like this, which I think site should feed into their reputation systems. (I talk about this in my article on Social Behavior Design.)
The problem with relying on people to ignore/block each other is that every new user has to have the same negative experiences with every bad actor before they can fine tune the site. It also provides little corrective feedback to the bad actor. Having said that, I think every social site should include these features; they’re invaluable for protecting people from non-systemic antisocial behavior like harassment from an ex.