I'm not sure how you define hacking. Web-scraping is not gaining unauthorized access to an otherwise inaccessible system. Anything you can see with your eyes in a browser is out in the open. And you can adjust a scraper's schedule to be mostly indistinguishable from human browsing habits.

That is, if a web-scraper can be reasonably indistinguishable from a human, then certainly we can't say web-scraping is illegal across the board.