I would argue there is a higher level of peer review that happens on Twitter at times than by some of the largest medical journals. You don’t see this high level of medical conversation on Facebook. Instead you get status updates about peoples miscellaneous thoughts or another invite to some random event you don’t plan on attending.
Further, Facebook doesn’t carry the medical conversation forward — it’s too declarative. Twitter is not.
Grown up medical conversations are happening on Twitter, not Facebook.