I would expect them to monetise through advertising and increasing engagement on the site by using linked services to make the whole site experience richer, thus leading to more ad views.
I might also expect Facebook to ask the services for some money to get their faces seen on the platform.
Is that hopelessly naive?
And how did you think they were monetizing in the first place? When I read all the outrage here, it’s almost like I’m reading comments from an alternate universe where nobody knew Facebook’s business model. On top of that, I find it even more amusing that lawmakers are up in arms over this, when they were the ones who passed the Patriot Act in the first place, destroying the Bill of Rights and desecrating the Constitution.