Yes, - and a lot of online communities on the internet has reached that scale. Facebook, Twitter, Instagram, Reddit...

In case of reddit, the problem is even more interesting. There are subreddits, so it is naturally segregated, and moderators and community are local. The communities can use downvotes to 'stone' an offender, and local elected moderators can enforce a ban. In case moderator or community mishandles the process, 'federal' admins can intervene. So we are pretty much at medieval level of justice there (much better than whatever constitutional dictatorship facebook and twitter have).