That is TERRIBLE advice. I don't know exactly what you mean by 'friendly hacking' but ANY exploitation of a website vulnerability without that site's permission would be a crime pretty much anywhere; even if it isn't malicious. It would be far from the first time that an administrator or owner didn't understand that the person was trying to help or just didn't really want to deal with it and it then just ended up being an issue of the vulnerability discoverer vs. law enforcement. Never a fun situation even if you win.