Registration by invitation

More and more often, exclamations are heard in the comments that the habr is no longer the one that users with strange and inappropriate behavior have appeared.
Do not you think that the site has gained enough users to close the open registration and go to the invitation system that is similar to dirty. You can select invitations based on karma or the results of voting for the post. This system is introduced on dirty.ru and has long proved its effectiveness. Now there are no effective methods to combat the appearance of inappropriate people. And I'm afraid that over time, clans of users will inevitably appear, as happened on Digg.com. Fighting them will be virtually impossible. It is even strange that so far no one has organized such a “social attack.” I see the main advantages of introducing registration by invitation, that it will be possible to improve the quality of the content of the habr and avoid the formation of groupings.