Is this bitcoin value fall an affect of this ban by FB?
It may not be the only reason but I would say it will surely have some impact on crypt market cap and ICOs as well.
No, facebook decision regarding banned advertisement for cryptos has nothing to do with the drop in bitcoin value, besides even before any announcement of facebook the value of bitcoin already dropping continuously. But I'm kinda sure this happenings can have a negative impact with regards to popularity of bitcoin as much as we want to tell people the good things behind cryptos thru social media, we are now prevented in doing so.