It is their right to ban ICO ads circulating on facebook. They only do this to clean their hands of possible ICO scams. But no matter what they do, facebook will never be the source of the real truth or whatever they are trying to show the masses now.
Facebook is banning those crypto advertisements because of the possible cause of this in their reputation, people are blaming the system for scam ICOs without thinking that it is not right to blame it in social media networks.