FB and Google each have considerably more influence than any news organization, because they own the algorithms that decide what people see, and what they don't.
The smallest change in those algs could influence election outcomes - remember, election outcomes are often very close.
The 'human' editors FB hired were shown to be heavily biased, not because of an organizational approach, but due to the individual biases of the people they hired. Which is why FB got rid of them.
It's just too easy for bias to introduce itself systematically in these orgs - even if there is no ill will intended.
It's hard enough when there's no over conflict of interest, let alone when there is.
The CEO of Exxon, Rex Tillerson, who is now sec of state, has divested himself of all Exxon shares, as he should.
If Zuck wants to govern, he can divest his FB shares and put his diversified holdings in a 'blind trust' as you say.