Legal and Ethical Considerations of Scraping Public Data

Just a question on scraping since I'm pretty new to it: If a website has in their ToS that you're not allowed to scrape them, what's your take on the legality and ethics of it if it is for public (no sign in required to view it or antyhing like that), non-personal info? E.g. seen that Y Combinator has in their website terms that you can't scrape them, but still see tools scraping their directory and workatastartup job board – this is public data that doesn't require login, but what's your take on it?