I think it's only fair for facebook to ban ads that feature bitcoins and ICOs because some ICOs are rich enough to trick people into buying into their scams. They even use bitcoins to entice their attention towards the possible investment growth they can get.
They actually ban Bitcoin and ICO related ads because the crypto currency scam that happened to twitter user while twitter was held responsible for it. Meanwhile, Facebook don't totally place ban on bitcoin or crypto currency related ads thats genuine.