In short, youre free to block ads, but interfering with the publishers right to serve or restrict access to copyrighted content in a manner they approve of (access control) is illegal. Facebook is one of the companies known for successfully fighting back hard against ad blockers.
Can you get banned for using adblock?
There has been no mention of accounts being banned that use adblockers, but there is a new term in the terms of service that states YouTube may prevent access if it believes, in its exclusive direction, that the provision of the service for you is no longer commercially viable.
Is using adblock on Crunchyroll illegal?
Stealing is illegal, so if adblock is stealing then it would be illegal but its a openly available addon for mozilla and as far as i know its available for chrome as well, if it was illegal then they would block it, but they dont so its perfectly legal.