Re: badly implemented
If this were in the UK the site operator would be obliged, once notified, to remove the offending material and attempt to enforce that it doesn't come back - been there. It was annoying at the time, but I'm not sure it's an unreasonable obligation all up.
Of course though in the US, rules are different - all hail the free market. But to my eyes the common carrier defence used by phone companies isn't really a neat fit when applied to a website which is already a) filtering on terms, this showing it can be done, and b) has been notified that some postings are in breach. No doubt the owners benefited from the advertising on the material that their lazy and/or incompetent asses allowed through.