It's important to distinguish between you being allowed to tell them and them being able to compel you to tell them. I see no problem with requiring a warrant for the second one.
[1] The subpoena ad testificandum dates back about 800 years.
This is also justifying the lack of a warrant requirement based on something that breaks the analogy to the original case. Witness testimony is no one's "papers and effects", unlike stored data.
Using a more accurate view of their model, it becomes clear that FB is strongly incentivized to keep their raw data to themselves. Failure to do so means risking that someone will not only beat them at their own game, but will do so at their expense. Same goes for Google, etc. So yes, it is perfectly reasonable to share a lot of very personal data with them while expecting that much of it will be carefully protected. After all, the stratospherically high value of their position depends on the inability of others to connect the very fine-grained demographic profiles they create with the specific individuals behind them.
Given this reasonable expectation of privacy, it makes more sense to see these third-parties more like doctors, priests, or accountants. Yes, they're all third parties too. But they're ones who we absolutely expect to protect our privacy. Given how deeply established the norms of confidentiality are in cases like these, I fail to understand why we we've acquiesced so readily to the fairly radical standard set in 1979.