Known and verified are two very distinct things. Does the public know that Facebook does this? Yes. Do they know it's harmful? Yes. Does Facebook also know this? Yes. Did they tell congress that they know this? No, in fact they told them the opposite.
The whistleblower is simply proving that unverified known - that Facebook has done research in its harm and knows they exist. Facebook would say "so what, we're doing stuff to fix it".
The most important part is the following: Facebook believes that its implementation for corrective actions of its harm is solely its responsibility. IMO, this is what is so dangerous and revealing. There is no one auditing other than taking "Facebook's word for it".
> Yes facebook allows some content that some would consider not to align with mainstream US narratives.
This is an incredibly disingenuous description of the situation. Facebook's own (non-public, now publicly leaked) research indicates that Facebook causes harm to teens mental health. The only "US narrative" here is the one backed up my the incredible amount of research supporting the growing issue of mental health in the US (and the world for that matter).
EDIT: To further my point and give you a comparison - when a similar thing happened with Tobacco the government was able to control behaviors by (1) forcing tobacco companies to put labels on their products and (2) tax tobacco such that it dissuaded customers to buy. Imagine if William Morris said "we know tobacco causes cancer so we've actively decided to sell 10 million less cartons of tobacco this year". No, they ended selling X million less cartons because of those two measures (among others).