Copyright law says otherwise. As for enforcing the law, you're right, it may be difficult for individual authors to move the needle. But that that doesn't mean it's ok for scrapers to violate the law.

As to what constitutes fair use, that's a whole other story: some scraping may be found to be legal while others may not. Benefiting monetarily from legally dubious scraping only makes that scraping look more infringe-y. Of course, nothing is settled law until a court decides.