[13years]

People do leverage Facebook's claims when they align with their own. You are probably right in that it doesn't directly change anyone's opinion that disagrees.

However, it does reinforce confirmation bias. Those that align with Facebook's viewpoint will be less likely to listen to other user's opposing viewpoints as the feel emboldened that they viewpoint has some official support.

So I think it has an indirect effect in that it weakens user to user influence.