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That is not a defense. If they publish on their own sites, they are liable to be sued. I have no sympathy if they were publishing full articles, or a significant portion of them. I do sympathize if they only posted small excerpts with links to the sources, which should fall under fair use.
Sites like FR, DU, etc., do NOT fall under this. The publishers need to send specifically-formatted DMCA takedown notices for content added by users. The DMCA is generally a bad law, and even the takedown notice provision has been abused (it needs strict minimum penalties for fraudulent notices), but in general the requirement of the notices is one of the few good things about the law. It is supposed to protect site operators from getting sued over the submissions of users; otherwise, it would be too dangerous for anyone to run a site that facilitates public discourse.