Some options:
1) Ban individual users for life - nice idea if anyone can explain how it can reliably be done
2) Close down new registrations
3) Introduce (maybe temporarily) very strict moderation - note here that if this is to be applied fairly then a lot more than the 'offensive' stuff would disappear. This thread ought to for example.
I know of a site where this has been done. Few of us would survive more than a day there - death by boredom.
Self-policing works. Despite all the shouting, note whose posts disappear and whose remain. Just stop shouting and quietly get on with reporting what you don't like.