First IANAL. But there are people building businesses on this kind of thing even though it's almost universally not allowed. Google is the most prominent -- the judiciary has decided that a different set of rules applies to Google v. smaller companies, so Google gets away with it. That's because they are massive and were probably able to pay bribes to the judges to get them to agree with them.

Usually if you C&D upon receipt of C&Ds, you won't get sued unless you actually damaged the site. I assume companies like import.io and Scrapinghub adhere to those. I know particularly in the case of Scrapinghub, they won't go behind a login to get something in order to try to avoid heat.

Fundamentally, however, anything that makes scraping a key component of its business model is a high-risk business under current US law. People can and have sued scrapers out of existence, often leaving a trail of screwed customers, laid off employees, and dejected founders owing huge liability judgments.