They do have the right to do this. But being a social media platform, they should know better. Social media sites are now for advertising purposes. They're just doing this to clean their hands off of possible scam ICO's. But no matter what they do, facebook will never be a true source of truth or whatever their trying to show the masses right now.
Yeah right, they have an authority to do it, to banned some ads that has not nothing to do with the social media itself like in Facebook. Facebook is a platform of social media and this will help you to communicate other people and also to show the world how or what did you experience in your daily life. Bitcoin ads has nothing to do with facebook but it can give also an information about the bitcoin through ads but make other things in appropriate way or manner. This bitcoin may lead us people in a good and better society because it can help us interms of financial. But i am not against with, but think about the people who does not know or want to see this ads. They will feel irritated from this.