I wouldn't say that Facebook is against Bitcoin but they are very cautious and trying to protect their users.
Having in mind how huge user network they have, they have some responsibilities. And the great deal of money that is coming from advertising. But some crypto adds might be connected with scams and they don't want to have anything with that or take some responsibility.
There are also some rumors that Facebook is going to launch its own currency although I don't believe much in that.