Why wouldn't they do it? If you had a backdoor into the brains of billions of people across the world (except China), and you were a billionaire with infinite ability to morally rationalize any behavior, what would stop you?
Zuckerberg doesn’t have a control panel where he can move sliders all by himself, any change in weight on the algorithm has to be implemented by a whole bunch of people, any of whom could leak to the press.
It’s not guaranteed it would happen by any means but it’s definitely something that would factor into a decision. Broadly I agree with you though, normally I’d say “extraordinary claims require extraordinary evidence” but I’m increasingly convinced the extraordinary claim here would be that they aren’t manipulating things to benefit themselves in some way or another.
They have their own DEI, affirmative action and cultural sensitivity teams who move the bias sliders based on their political viewpoints and on what management tells them depending which of the political groups they need to pander to: "Let's move the slider to the left to make sure Trump doesn't win; Oh shit Trump won, quick, move the slider to the right".
>any of whom could leak to the press
That's why they sign NDAs.